carb tuning info and links



carb tuning info and links

Postby grumpyvette » September 17th, 2008, 10:43 pm

it helps a great deal to know what your working with ,ID suggest starting, by verifying TDC and having the correct timing tape on your damper then,start with 8 degrees btdc and verifying the full advance of 36 degrees total is all in at 3200rpm as a base line, once youve got that, as a standard you can tune and run the car and eventually try tweaks to the basic ignition curve if needed, once you have an ignition base line, move on to the carbs tuning, you also need to keep in mind that what goes in as a fuel /air mix needs to go out as a much expended volume of hot gases and a restrictive exhaust will effectively block most attempts to get more power from an engine, so measure exhaust back pressure. you might be amazed at what a couple hours research into the subject will do to help you build a much more durable engine, and actually reading thru links and sub-links and asking questions helps a great deal
[b]you might be amazed at what a few tests with a fuel pressure gauge can tell you
ILL point out a few factors a fuel/air ratio gauge is a big help as is an INFRARED TEMP GUN,
be very sure to verify the plenum vacuum and exhaust back pressure, as both vacuum leaks and clogged exhausts or clogged catalytic converters are a frequent source of problems

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you might be amazed at the number of times "CARBURETOR PROBLEMS" are cured with getting the IGNITION, TIMING AND ADVANCE CURVE WORKING CORRECTLY, and check out the simply things your 100% sure you did correctly, because I can,t begin to tell you how many times I see guys who have the firing order on the ignition wrong, or guys that install a 4/7 swap cam and still use the standard ignition firing order or guys that never verify TDC and ignition advance curves.
get an IR temp gun and check for wild variations in exhaust temps, get a compression test done, do a logical check to verify each cylinder fires etc.
[/b]
Ive found its a whole lot faster to use a quality IR temp gun, to locate a individual cylinder that's mis-firing as it tends to run significantly cooler than adjacent cylinders, or hotter if its a vacuum leak at times, as lean F/A mixes tend to run hotter
(Ive used this one for years)
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http://www.professionalequipment.com/ex ... ermometer/
Wide temperature range from -58 to 1832°F (-50 to 1000°C)

many temp guns don,t read high enough or accurately enough
http://www.professionalequipment.com/ex ... ermometer/
that you can use on the engine to check ALL 8 exhaust temps, individually, this quickly locates plugged injectors or vacuum leaks ETC
Wide temperature range from -58 to 1832°F

when selecting an IR gun for automotive use, you really want to be able to read from 0 F deg-about 1400F deg. to cover most conditions you'll test for
READ THRU THESE RELATED LINKs YES I KNOW YOULL WANT TO SKIP OVER THEM< BUT YOULL MISS A GREAT DEAL OF INFO DOING SO!
viewtopic.php?f=56&t=495&p=613#p613

download/file.php?id=1710

http://autospeed.com/cms/A_111456/article.html

http://www.innovatemotorsports.com/products/lm2.php

http://www.vintagemusclecarparts.com/pa ... seat1.html

http://www.holley.com/data/TechService/ ... 20Info.pdf

http://www.thecarburetorshop.com/Troubleshooting.htm

http://members.tccoa.com/392bird/tuning.htm

http://www.edelbrock.com/automotive_new ... vids.shtml

http://www.international-auto.com/fiat- ... gauges.cfm

http://www.summitracing.com/expertadvic ... Calculator

http://www.thecarburetorshop.com/Troubl ... rdstarthot
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WHEN TESTING<be sure the fuel pressure gauge reads correctly by comparing it to a second test gauge, these fuel pressure gauges are frequently defective
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watch this
http://www.youtube.com/watch?v=UYGU7mTwsZc
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READ THE LINK
viewtopic.php?f=50&t=268&p=18435#p18435
a few hours spent reading links and sub links should help

viewtopic.php?f=50&t=268&p=18434&hilit=wide+band#p18434

viewtopic.php?f=27&t=3096&p=18612&hilit=wide+band#p18612

viewtopic.php?f=32&t=6011&p=18597#p18597

viewtopic.php?f=57&t=4974&p=13868&hilit=infrared#p13868
read these links

viewtopic.php?f=55&t=1790&p=4544#p4544

viewtopic.php?f=70&t=1809

http://www.chevyhiperformance.com/techa ... 0_cfm.html

viewtopic.php?f=57&t=4701

http://www.corvettefever.com/techarticl ... ing_guide/

viewtopic.php?f=70&t=962

http://www.jetsrus.com/FAQs/FAQ_rejetti ... _carb.html

viewtopic.php?f=55&t=9326

viewtopic.php?f=55&t=8126&p=28205#p28205

http://www.ehow.com/how_7570346_calcula ... r-cfm.html

viewtopic.php?f=70&t=875

viewtopic.php?f=55&t=264&p=1301#p1301

http://www.carcraft.com/techarticles/cc ... ewall.html

viewtopic.php?f=44&t=5575&p=16927#p16927


How to use a vacuum gauge to troubleshoot: http://www.secondchancegarage.com/public/186.cfm

Go the techincal tab and look up vacuum gauge info here: http://www.centuryperformance.com/upgrade.html

viewtopic.php?f=55&t=2994&p=7857#p7857
many carb tuning issues are really basic fuel supply issues, if you can,t maintain a consistent flow at a constant pressure to the carbs feed the car will more than likely have tuning issues

viewtopic.php?f=55&t=10310

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viewtopic.php?f=55&t=211

viewtopic.php?f=55&t=635
each carb has good and bad points, and most guys get into trouble by not following a logical step by step approach, where they verify the fuel pressure,is between 4.5 and 6psi, throttle linkage, fully opens, and youll want to know the carbs vacuum connections are correct, and what your vacuum gauge reads both at idle and at wide open throttle and youll need to verify the float levels are correctly set and verify theres no vacuum leaks on the intake or carb gaskets as a first step , youll want to verify the ignition works and the timings correct, it advances and that the valves are adjusted so you don,t spend time fighting a "CARBURETOR PROBLEM" that has NOTHING to do with the CARBURETOR!learning to read spark plugs and correctly using a timing light, correctly adjusting the valve train and use of a vacuum gauge will help a great deal, if you happen to own a infrared temp gun that's occasionally a big help in diagnosing problems


Id check the float level then change the accelerator pump diaphragm ,watch these

http://www.youtube.com/watch?v=X2W0blhIrug

http://www.youtube.com/watch?v=5_lgTTkXJDM



http://forums.holley.com/entry.php?428- ... or-Stumble


Off Idle Stumble - A Holley Carb Review wrote:
I installed a GM crate engine in my 79 Vette a few months ago. The engine came with a 650 CFM Holley 4-barrel carb. During break-in, the engine seemed to run fine. I then had a less restrictive dual exhaust system installed on the vehicle. It was about that time that I noticed an off idle stumble, or flat spot, begin.

At first I began adjusting the easy and basic stuff - timing, carb float levels, fuel/air mixture, vacuum advance ports. When I still experienced a dead flat spot on full throttle from idle or low RPM's, I read technical articles on the Holley carburetor.

A dead spot from idle or part throttle to full throttle, especially if the flat spot is accompanied with a back fire through the carb is an indication of an overly lean fuel/air mixture or insufficient fuel delivery during wide open throttle, or "WOT".

A racing buddy suggested that the "squiters" were too small and not providing enough fuel during the transition from idle/part-throttle to WOT. He also noted that the secondary valves were not opening at any RPM. The Holley carb had .31 squirters so I bought the next size up (.35) and installed them in the carb. The engine bogged terribly so I put the .31 squirters back in.

Next, I installed a "quick change" secondary vacuum valve/spring mechanism. The stock mechanism requires a fair amount of time to disassemble and replace the secondary vacuum springs with springs of different tension and operating ranges. I found the crate engine Holley carb came with the strongest spring available that never allowed the secondaries to fully open. If you want to have some inexpensive fun trying to improve your mid to top end response, I would recommend that you buy this quick change secondary vacuum kit and experiment with the 7 or 8 different springs that you can purchase in a separate kit. You really can dial in good performance in a matter of a couple of hours - if you have the quick change kit. Well, I ended up with a spring that was two steps lighter and faster responding, but this did nothing to help the dead spot off idle/part throttle.

My next step was to switch the vacuum hose from the distributor to every known vacuum port I could find. I thought that I may have a vacuum or timing problem so I spent hours switching the vacuum hose and taking test drives to measure the change in performance. No improvement in idle/part throttle response.

The next item I attacked was the adjustment bolt on the accelerator arm that presses against the power valve actuating arm on the left front side of the Holley carb. You can adjust the length of the bolt by tightening or loosening the adjustment nut. I tightened and loosened this darn nut/bolt set-up and sometimes it would help and other times it would be worse, but nothing corrected the backfiring through the carb and the flat spot response.

I then read an article that suggested a 50cc accelerator (power) valve would solve the off throttle flat spot. The kit cost $44 and basically is a larger reservoir of fuel to squirt into your carburetor when you transition from idle to running throttle. I hesitated installing this unit as the 30cc volume of the stock accelerator valve should be sufficient for the crate engine V-8. I decided to review other options.

I read about the different profile plastic cams that Holley carbs use and thought I would experiment with these. I swear Holley makes more money on these various carb tuning kits and parts than they do on the carb itself. After removing the stock orange cam from the throttle linkage and examining it's profile, I discovered that it had two mounting holes marked "1" and "2". By the rub marks left on the cam from the actuator arm on the carb, it appeared that the cam could be reversed to have the steeper and more aggressive side of the cam actuate the arm that in turn presses the accelerator arm that presses the accelerator pump valve that squirts raw fuel into the primaries during the transition phase from idle to throttle. At the same time, I thought I would replace the #65 main jets with something a little less restrictive, so I installed a pair of #67's.

One last adjustment I made was to eliminate any gap or slack between the bolt on the throttle actuator arm and the accelerator pump actuator arm. I figured that if there was any "slop" or gap between these two pieces, the throttle would begin it's opening without making contact with the accelerator pump valve actuating arm ... this would cause a delay in delivering more fuel during the initial opening of the primary valves and this would produce a lean mixture, backfire and stumble.

After installing slightly larger main jets, adjusting the throttle cam to a more aggressive slope/timing and eliminating the slop between the throttle actuator arm/bolt and the accelerator valve pump arm ... the engine ran fantastic. NO stumble. No back fire through the carb. No hesitation in acceleration from idle/part throttle to WOT.

If any of you are having trouble with flat spots & backfiring with your Holley carb, you might try the simple adjustments that are easy to do and don't cost much. The main problems I had were an incorrect throttle cam and a poorly adjusted contact between the throttle arm and the accelerator pump (or "power valve")actuator arm on the Holley carb.

I returned the $44 50cc accelerator pump valve. The pair of main jets cost $6.44, but I probably didn't need those. The cam adjustment made the biggest improvement and that was free - just flip it over and use a different mounting hole. And finally, adjusting the actuating arm was very helpful and cost nothing.

So before you give up or spend allot of money chasing Holley carb problems like mine, try the simple and inexpensive adjustments before you invest in expensive upgrades. Hope this helps.


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EDELBROCK
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HOLLEY
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QUADRAJET

viewtopic.php?f=55&t=1144&p=2310#p2310

as Im sure your aware the best torque will usually be with a ratio of about 12.5:1-13:1 and the most fuel efficient ratio will be closer to 14.7-15:1
carbs react to CHANGES in air flow rates, to change the fuel feed rates so theres always a delayed reaction, EFI generally uses sensors to detect BOTH changes in AIR/FUEL RATIOS in the exhaust and changes in vacuum and airflow rates
carbs generally cover up sudden increases in air flow such as stomping on the throttle to WOT from idle with a long shot of fuel from the accelerator pump and power valves adding extra fuel, neither one is a precisely metered response.
you can tell a good deal about the conditions in an engine if you know the vacuum readings (use a gauge), and know how to read spark plugs
now I use a vacuum gauge a timing light, and an IR temp gun on the headers along with the data from reading the plugs and the a/f ratio sensors, each adds to the indications of whats going on, yes you can achieve a 14.:1 ratio and get the engine to run decently, but in most cases it will tend to run better in the low 13:1 ratio range during transitions and about 14:1-14.7:1 during cruising simply because theres always a tendency to go lean during sudden transitions with most carbs.
Id keep in mind that going rich during rapid transitions is preferred over going lean and getting the a/f ratio stable and predictable at cruise and idle and during mild acceleration like on the freeway,where you'll spend 90% PLUS of your time is far more important than temp swings during throttle changes, or during WOT where running slightly richer, during high load high rpm conditions is preferred simply because it makes better power and has less tendency to run into detonation, especially since you'll spend far less time under those conditions

http://www.holley.com/TechService/Library.asp
BTW (lots of links and sub links on carb tuning, spark plug reading, etc.)
if you do some searching on the hybridz site,
but heres a bunch

http://www.goldrush.com/~rhuish/temp_data/carbtune.html

http://www.bob2000.com/carb.htm

http://www.centuryperformance.com/tunin ... g-148.html

carbs and tuning info, read all the links and sub links


http://www.secondchancegarage.com/public/186.cfm

http://www.centuryperformance.com/tunin ... g-148.html

viewtopic.php?f=55&t=635

viewtopic.php?f=55&t=1442

http://www.chevyhiperformance.com/howto ... index.html

http://www.chevyhiperformance.com/tech/ ... index.html

viewtopic.php?f=44&t=773

http://www.thecarburetorshop.com/Troubleshooting.htm

http://www.holley.com/TechService/Instr ... ry=&page=4

viewtopic.php?f=50&t=6174&p=20791#p20791

viewtopic.php?f=70&t=875

viewtopic.php?f=70&t=1015

http://www.youtube.com/watch?v=eiRIfcrc ... _embedded#

viewtopic.php?f=81&t=1189&p=2447#p2447

viewtopic.php?f=55&amp;t=211

viewtopic.php?f=55&amp;t=1961

viewtopic.php?f=55&amp;t=2940

viewtopic.php?f=55&amp;t=1639

viewtopic.php?f=55&amp;t=264

viewtopic.php?f=44&amp;t=1788

viewtopic.php?f=44&amp;t=579&amp;p=743&amp;hilit=infrared#p743

http://www.bgsoflex.com/holley.html

viewtopic.php?f=55&t=1961&p=5203#p5203

http://www.classictrucks.com/tech/0806c ... index.html

viewtopic.php?f=55&t=1442&p=5524#p5524

http://www.mortec.com/carbs.htm

http://www.youtube.com/watch?v=k-Nx5HEzvlY

http://www.mortec.com/carbtip1.htm

http://www.summitracing.com/parts/MOR-65222/?rtype=10

http://www.shockley.net/holley-jets.asp

http://www.chevyhiperformance.com/howto ... index.html

http://www.nastyz28.com/perftune.html#carb

http://www.digitalcorvettes.com/forums/showthread.php?t=77602

viewtopic.php?f=44&t=777&p=1127#p1127
(huge amount of linked info in this link)

BTW use a 190F T-stat and an extra electric fan that comes on at 200F to keep the engine coolant temp stable, try to keep the oil temp in the 215F-220F range if you can,to burn off moisture that can form acids over time in the oil, and the fuel pressure stable at about 5 PSI,, have no more than 1-1.5 psi of back pressure in the exhaust at WOT, it makes tuning far easier, make sure the ignition timing curve is smooth & consistent, and do a leak/down test and adjust the valves, do a vacuum leak test, check the oil pressure,and fuel filter, to make sure your not working with mechanical problems.
if your tuning an n/a engine and the IR gun shows header temps over 1250F or under about 1100f once its up to temp, you'll generally find vacuum leaks, ignition curve problems or a/f ratio problems
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obviously you need to have a consistent base line advance curve to work with,
on most Chevy v8 engines that run cams designed for street/strip use Ive generally found a advance that goes from about 8 degrees at idle speed (800-900rpm in most cases) and smoothly advances the ignition to about 36 degrees or about 28 degrees advance from where it started at to reach 36 degrees at about 3200rpm , is generally a good place to start, or about 82 degrees advance per hundred rpm, you can then play with the engine and determine what changes MIGHT be required.

standard vacuum connections
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http://www.secondchancegarage.com/public/186.cfm

manifold to power brake booster
manifold to distrib vacuum advance
pvc to carb or air cleaner assembly
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I ran ac-crossed this chart that might prove useful as a rough guide, and don,t forget this thread, and ITS sub-links


ILL point out a few factors a fuel/air ratio gauge is a big help as is an INFRARED TEMP GUN,
be very sure to verify the plenum vacuum and exhaust back pressure, as both vacuum leaks and clogged exhausts or clogged catalytic converters are a frequent source of problems

Ok Ive got one and have tested several of them.

viewtopic.php?f=4&t=1337&p=2921&hilit=+infrared#p2921

http://www.3barracing.com/product_3.htm

http://www.rbracing-rsr.com/rsrgauge.htm

http://www.scirocco.org/tech/misc/afgauge/af.html

http://www.innovatemotorsports.com/products/lm1.php

http://thedynoshop.net/prod01.htm

viewtopic.php?f=50&t=1853&p=4848#p4848

heres my take on them, short answer, they are a big help but a P.I.T.A. to set up and use if your not going to semi permanently install them on your car.


IVE come to use reading spark plug condition,

http://www.digitalcorvettes.com/forums/showthread.php?t=80783

http://www.digitalcorvettes.com/forums/showthread.php?t=85537&highlight=plugs

use of a good timing light and vacuum gauge , fuel pressure gauge and use of a GOOD HIGH TEMP INFRARED THERMOMETER (THIS ONE)

http://www.professionalequipment.com/extech-high-temperature-infrared-laser-thermometer-501-ds-42545/infrared-thermometer/

as a very quick to use and accurate set of tools. :thumbsup:

OK WHY???

well your main concern when tuning an engine is to keep the all the cylinders running approximately the same ratio and at about 12.8:1 for max power up to about 14.7:1 for low emissions and good mileage,

so whats the advantage/disadvantages

a fuel air meter uses a o2 sensor, if you place it in the header collector it gives an AVERAGE of all the cylinders on that cylinder head,If theres an (X) installed close to the dual collectors reversion pulses can occasionally even give data from the other side of the engine, so in theory and in practice you can have two cylinders run lean and two rich and the AVERAGE tends to look RICH to the O2 sensor as it SEES unburnt fuel, if you place it in the individual primary header tubes you either need eight O2 sensors (VERY EXPENSIVE, and keeping the wires from burning or grounding outs a TOTAL P.I.T.A......IF you don,t succeed you destroy the O2 sensor and need to replace it.) or you need to be constantly swapping very hot and fragile O2 sensors and bung plugs constantly, but with the IR thermometer you can almost instantly see which cylinders are running hotter or cooler and adjust the jets or look for vacuum leaks, or other CAUSED for the TEMP DIFFERENCE, ETC, far faster too get all the cylinders running at approximately the same temp, indicating the same fuel air ratio, youll be amazed at how close the temp follows the fuel/air ratio, and you can confirm it with plug condition and the other test equipment. run any cylinder too lean and detonation can break rings or melt pistons, run it too rich and you can wash the oil off the cylinder walls and ruin rings/scuff pistons, you need to know whats going on in EACH CYLINDER not the AVERAGE of all cylinders.

SO, if your going to install a decent wide band fuel air ratio meter on your car thats fine, its going to be an asset to your tuning skills, if you install the indicator/gauge inside the car and weld in a couple extra bungs in the collectors for tuning and wide band O2 sensors which are a big help, but you will quickly find that its a P.I.T.A. to use it for tune ups on all your buddies cars with the welding collector bungs and installing plugs and O2 sensors while the IR thermometer route is fast and very simple and you can confirm with plug reading the condition of the engine.

YEAH! theres meters that you can stick in a tail pipe, but they read THE AVERAGE, not the individual cylinders ,
think about AVERAGEs
AS my old physics proffesor once said,
IF, I pour molten lead in your front slacks pockets and pack your butt in solid with DRY ICE,.... ON AVERAGE your comfortable:D

without a fuel pressure gauge and an adjustable return style fuel pressure regulator with a return line installed your basically restricted to guessing, and chances are very good youll have major problems, you need the engine timing set correctly and you need to learn how to tune carbs and correctly read spark plugs
step one is getting the fuel pressure rock steady at 5 psi, then get the carbs floats and jets set correctly, so you get plugs that look like this

good
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too lean
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too rich
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its amazing what you can learn about engine combustion chamber conditions, air/fuel distribution and temps, from reading spark plugs

viewtopic.php?f=70&t=5428

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=211

http://forum.grumpysperformance.com/viewtopic.php?f=55&t=635

http://forum.grumpysperformance.com/viewtopic.php?f=70&t=202

http://forum.grumpysperformance.com/viewtopic.php?f=70&t=1015
" IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
grumpyvette

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Re: carb tuning info and links

Postby grumpyvette » December 5th, 2009, 9:00 am

just a question, I see these discussions on selecting carb sizes frequently, but IM amazed at how rare it is for someone to actually hook up a quality vacuum gauge, or data logger, and an air/fuel ratio gauge to the plenum and header collectors have some buddy log the true air pressure readings in the plenum and f/a ratio as the car travels thru the track. now thats always been my approach,naturally you need to have a known ignition advance and a steady fuel pressure etc, and reading plugs and use of an INFRARED TEMP GUN on the headers just after a run looking for some consistency in temps doesn,t hurt with that info added
generally Ive found that if your WOT vacuum drops in the plenum , as your running thru the lights to between 1" and 0.5"going to a larger carbs, rarely going to give any noticeable gains, and generally keeping the f/a ratio in the engine at the top end of the track to in the 12.5-13:1 range will produce the best times, but Ive only had 40 years doing this stuff and IM still learning and wide open to suggestions

viewtopic.php?f=55&t=1038&p=4014&hilit=spacers#p4014

viewtopic.php?f=57&t=4974&p=29925&hilit=INFRARED#p29925

the fuel/air ratio is only one factor, the intake runner placement in relation to the carbs venturies and the vacuum reading in the plenum and the rate of change in that vacuum during any transition from the primaries alone to all four venturies will effect the results, as will the accelerator pump shot volume and duration.
quadra-jets , generally have decent economy on the primaries, and good low vacuum reading in the plenum at full open throttle
but they are designed mostly for economy, and while they provide the required air flow for w.o.t. operation to provide good peak hp the much larger rear venturies generally DON,T provide the same precise metering that CAN, be achieve with a properly tuned square bore carb
Ive tuned both carb designs for many years and while both can provide both decent economy and peak hp I,d be surprised if you find many people that can tune a q-jet to smoothly transition at mid throttle under all conditions as smoothly as a good Holley or demon, its just easier to tune 4 nearly identical size venturies ,that transition smoothly as to the air pressure changes in the plenum that are roughly centered over a plenum,than two sets of vastly different cross sectional venturie areas, that rapidly reduce the vacuum in the plenum and use a large volume of fuel from the accellerator pump circuit to compensate.now obviously a slow transition from just the primaries to w.o.t. allows both designs to compensate reasonably smoothly, but go from cruise to w.o.t. by stomping on the gas pedal and theres a difference in the metering quality of both designs and how they maintain the plenum vacuum and f/a ratio.
keep in mind fuel/air ratio, will be the same if the amount of fuel and air is the same, but if one carbs throwing a fine mist and the others, provided a gulp of air mixed with a stream of fuel the power results will vary

ignition timing thats a bit to retarded will tend to make the plugs run cold and foul, setting your float levels and making 100% sure the linkage functions correctly is mandatory, before you start chasing problems

http://www.barrygrant.com/bgfuel/default.aspx?page=83

http://www.stockcarracing.com/techartic ... index.html

http://www.corvettefever.com/techarticl ... index.html

http://www.holley.com/data/TechService/ ... uretor.pdf

viewtopic.php?f=80&t=8505&p=29830#p29830

unscrew the site plugs and adjust the floats until the fuel level just prevents fuel flow from the site holes at idle, youll need a flat blade screw driver and a 5/8" wrench
http://www.chevyhiperformance.com/techa ... 0_cfm.html
if you read thru the link above, very carefully youll find the 750cfm -to 830cfm carbs made the best average power, on that 383 sbc, so if we average the results lets say an 800cfm might have been near ideal.
now you might think.... ok,
800cfm/383 cubic inches =2.09 cfm per cubic inch of displacement,
so logically a 454 big block x 2.09=948cfm.....,
or a 327 x 2.09= 683 cfm,
but the truth here is that a skilled and experienced engine tuner can get a 950cfm or a 750cfm carb to work remarkably well on either the 383 0r 454 engine.
that 2.09 cfm per cubic inch of engine displacement will get you "in the ball park" but its your ability to tune the carburetor to match the application , far more than the rated carb size thats much more critical to matching the carb to the engine.

QUESTION How do I adjust the fuel level on my carburetor?
ANSWER Setting the fuel level should be the first thing you do before attempting to make any further adjustments.The float level should put the fuel level just below the bottom of sight plug hole. You will make the adjustment with the vehicle on a level surface and the engine idling. You will first remove the sight plug, then to make your adjustment you will need to loosen the lock screw on the needle and seat. This will allow you to turn the adjusting nut to raise or lower the float level. Each hex flat on the nut will change the float level approximately 1/32". When you have the fuel level just below sight plug hole you will then tighten the lock screw and reinstall the sight hole plug. Make sure you have a shop towel handy in case you have any fuel leaks from the Sight plug or needle and seat adjusting nut.

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NOT ALL HOLLEY AND GENERIC BOWL GASKETS INTERCHANGE
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50cc PUMP

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YOU CANNOT JET OUT A MOMENTARY LEANNESS CAUSED BY AN INSUFFICIENT FUEL SUPPLY IN YOUR CARBS FUEL BOWLS, THE WRONG POWER VALVE,OR ACCELERATOR PUMP CAM, or the CARBS TRANSITION CIRCUIT THAT WILL NOT SHOW UP IN A NORMAL PLUG COLOR READING. !!!

viewtopic.php?f=80&t=8505&p=29830#p29830

if the fuel level won,t adjust, it
sounds like a needle valve needs replacement, or a carb floats defective

SIMILAR TO THIS

http://www.summitracing.com/parts/HLY-6-513/
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http://www.summitracing.com/parts/HLY-6-519-2/

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http://www.summitracing.com/parts/HLY-116-10/
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viewtopic.php?f=44&t=773

viewtopic.php?f=50&t=1853&p=4848&hilit=ratio+meter#p4848

viewtopic.php?f=50&t=1853&p=4848&hilit=+air+fuel+meter#p4848

viewtopic.php?f=50&t=2891&p=9279&hilit=plugs+ratio#p9279

viewtopic.php?f=44&t=773

viewtopic.php?f=50&t=383&p=2301&hilit=+power+valve+vacuum#p2301

viewtopic.php?f=44&t=777&p=4546&hilit=+power+valve+vacuum#p4546

viewtopic.php?f=55&t=1790&p=4544&hilit=+holley+cam+pump#p4544

viewtopic.php?f=55&t=1639&p=4545&hilit=+power+valve+vacuum#p4545

THESE THREADS above SHOULD HELP



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http://www.daytona-sensors.com/tech_tuning.html
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If you want your engine to start up easily,you start with a nice hot blue spark at the spark plugs and the correct ignition timing curve, for that in most cases youll need a good alternator, battery with at least 13.5 volts and a decent electrical ground, you might want to keep in mind cool gasoline, as a liquid doesn,t burn well at all, its gasoline vapor mixed with air thats extremely flammable,and its heat that tends to aid vaporization, and to get fuel to form a vapor you need either high pressure in the fuel system to form a mist spray like an injector, does in the intake runners or high air speeds, and high compression ratios to build that heat on the compression stroke,and a strong ignition that promotes the mix to ignite, resulting in a rapid increase in engine heat, or some other method of increasing the engines ability to mix cool fuel in liquid form into the air flow to form that easily ignited vapor.

your carb should have a choke that both restricts air flow and increases air flow port speeds and richens the fuel air ratio, as the vacuum the carb sees is increased
for ease of ignition youll want a fairly rich ratio near 12.8:1, but best economy is found closer to about 14.8:1 ratio,
once an engine kicks over it spins faster and as the air flow thru the ports increases so does the percentage or amount of fuel that forms a vapor and that results in more heat generated, its a cycle.

a strong starter,backed by a large battery that spins the engine fast, high compression, that quickly builds cylinder heat and a retarded low speed ignition point so the engine is not fighting a great deal of pressure build-up before t.d.c. all promote an easier start-up



http://en.wikipedia.org/wiki/Carburetor

How to tune a carb with a vacuum gauge.
http://www.centuryperformance.com/tunin ... g-148.html


How to interpret a vacuum gauge.
http://www.secondchancegarage.com/public/186.cfm


thoughts guys?

if you have a wide band oxygen sensor youll generally want to try to get into the 12.7-13.5 fuel/air ratio band, any leaner tends to get into detonation, any richer tends to get into ignition problems,but supercharged and turbo engines tend to run better on the rich end of that fuel air ratio, and many issues are related to not enough spark energy and heat or incorrect spark timing
but start by getting the ignition advance curve consistent.
then verify your getting both constant fuel pressure and volume, as a drop in either can cause problems.
maintaining a rock solid and consistent fuel delivery is a frequently over looked issue.

viewtopic.php?f=70&t=4683

viewtopic.php?f=55&t=635

viewtopic.php?f=55&t=109

viewtopic.php?f=55&t=211

viewtopic.php?f=55&t=1961

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Re: carb tuning info and links

Postby grumpyvette » April 29th, 2010, 7:18 pm

factory jetting info
http://www.holley.com/data/TechService/ ... isting.pdf

HollyPartNumberLocation.JPG


http://www.holley.com/data/TechService/ ... erence.pdf

HollyPNInfo.jpg



http://www.bgsoflex.com/holley.html

http://www.angelfire.com/fl4/pontiacdud ... lator.html

http://www.angelfire.com/fl4/pontiacdud ... lator.html
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these come in handy

http://aeromotiveinc.com/wp-content/upl ... ter-NN.pdf

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first youll want to verify theres no vacuum leaks,youll use a un-lighted propane torch not any flammable sprays as its far more precise, as you can stick the torch tip exactly where you suspect leaks,and it less messy and leaves no residual crap on the engine.
ITS important to understand how and why things work,IF you don,t have a timing light, generally you use a vacuum gauge on a STOCK engine to set timing by hooking it up to plenum vacuum , set the idle to normal idle speed (usually 670rpm-850rpm)and adjust timing to max vacuum reading, this DOESN'T,T ALWAYS result in the best possible timing but it will generally be fairly close on a DEAD STOCK ENGINE

YOU CANNOT JET OUT A MOMENTARY LEANNESS CAUSED BY AN INSUFFICIENT FUEL SUPPLY IN YOUR CARBS FUEL BOWLS, THE WRONG POWER VALVE,OR ACCELERATOR PUMP CAM, or the CARBS TRANSITION CIRCUIT THAT WILL NOT SHOW UP IN A NORMAL PLUG COLOR READING. !!!

Common Fuel Delivery Mistakes and How to Correct Them
by Barry Grant Inc. ©2004

Fuel lines, filters, pumps, and regulating devices exist to deliver gasoline or alcohol from the fuel cell to the carburetor, and in a bypassing system return it to the fuel cell. Pressures and volumes vary depending upon the kind of fuel used (gasoline or alcohol) and the type of fuel system employed. With routine maintenance, a good fuel system will pay dividends; yet many cars are fitted with systems that fall below the necessary standards. With a little help from BG Fuel Systems of Dahlonega, Georgia, here is a list of the most common mistakes in competition fuel systems and a guide as to how to correct them:

1. Incorrect fuel lines
Do not use 1/4" - 3/8" o.d. lines on a racing fuel system between the fuel cell and the pump. Racers often joke about their first race car and how the fuel line was so small it functioned as the main jet. Ensure the fuel is supplied through lines that are of the correct size for the application. Remember fuel line size is determined by the system, not the vehicle! Push-Lok, stainless steel braided hoses, and aluminum tubing are the most common fuel lines used on race cars.

2. Right-angle hose-end fittings from the pump to carburetor
Avoid forged 90*elbow fuel fittings as much as possible. Although they are inexpensive and readily available, they're restrictive and frequently cause fuel flow troubles. Hose ends with angles of 90* & 45* should also be avoided if possible. Nonetheless, should it become necessary to use one, use radiused hose ends (90* bends) as they have much better rates of flow. They're manufactured from aluminum, equipped with swivel ends for a positive seal and are easy to install.

3. Fuel pumps unsuitable for alcohol
An alcohol fuel system differs from the gasoline alternative in several crucial respects. Fuel pressures in a gasoline system are typically maintained between 7- and 9-psi throughout the rev range, whereas alcohol carburetors require low pressures of around 4- to 6-psi at idle and 9- to 11-psi at fully open throttle. This is necessary to prevent the carburetor from flooding at idle and under light engine load, yet maintain the extra volume necessary for maximum acceleration. Engines producing around 500-hp can be fueled with a 15-psi mechanical pump in conjunction with a throttle bypass valve. However, for engines over 500-horsepower, a belt-driven system with a diaphragm valve, or poppet bypass should be considered. For overall reliability and performance, a belt-driven system is usually the better choice. When using a diaphragm bypass, BG Fuel Systems recommend it be installed close to the carburetor for faster response.

4. Incompatibility between bypass and pump
Throttle bypasses were designed to operate with block-mounted pumps and, similarly, diaphragm bypasses with belt-driven pumps. Never use a throttle bypass with a belt-driven pump - they must function in pairs and are not to be mismatched.

5. Unsuitable fuel filter
Fuel filters with conventional paper elements must not be used with alcohol. Because alcohol absorbs water, the paper and the bonding materials deteriorate quickly. As a consequence, particles can enter the float bowls, or get stuck in the needles-and-seats and main jets. Further, it's equally important on alcohol applications, to avoid filters with inadequate flow rates, and inlet and outlet sizes that are too restrictive.

6. Neglecting routine maintenance on an alcohol system
Although alcohol fuel additives can help prevent corrosion and provide lubrication for pumps and other components, alcohol can severely corrode metal objects, especially aluminum, if allowed to remain in contact too long. There is no substitute for a strict maintenance program, it will not only prolong the life of the carburetor and fuel system, but also keep it trouble-free. Alcohol will naturally absorb water from the air. This not only dilutes the fuel, but also adds to the corrosive effects of alcohol. After every race, the alcohol should be drained from the race car and stored in air-tight containers; a vented fuel cell is not considered an appropriate storage container. The fuel system and carburetor should also be thoroughly drained and flushed of any residual alcohol. Some racers will add gasoline to the empty fuel cell and run the engine until they are certain the carburetor is filled with gasoline. Other methods include removing the carburetor and flushing it with a cleaning solvent or lubricating aerosol sprays. Removing inlet and outlet fittings from the pumps, bypasses etc. and lubricating the internals is also an acceptable practice. Whatever the method, maintenance on an alcohol system is crucial; ignore it and the system will fail.


7. Failing to use a high-flow air cleaner
Race engines rely on receiving air as well as fuel, but are frequently starved by the use of thin, small-diameter air filters that are detrimental to their performance. If possible, use a filter that is 14"diameter x 4"tall. If clearance is at a premium get one with a recessed pan, which allows for deeper filter elements. Get a good quality air filter. If you're constantly cleaning lots of dirt from the surface of your race car the chances are your air cleaner is struggling to filter the dirt and debris from your engine.

8. Deterioration of foam-filled fuel cells
Modern military-spec foam-filled fuel cells, are compatible with conventional fuels, racing fuels and alcohol. However, alcohol can cause the foam to deteriorate and it must be renewed once a year. To check the condition of the foam, simply remove the cap and pinch it between finger and thumb. If pieces come away the foam must be replaced.

9. Not having proper linkage travel and return springs
Make sure that, at wide-open throttle, the butterflies of the carburetor are fully open. Use a minimum of two, good quality return springs - preferably of stainless steel and employ them, if possible, in two different places on the linkage. Ensure the linkage and the return springs operate without interference throughout the full range of throttle travel.

10 Failure to use an adjustable pedal stop.
It's amazing to consider the large numbers of race cars that have no form of throttle-pedal stop, and inexcusable that so many are permitted to compete. Excessive loadings on the linkage, carburetor shafts and butterflies can cause the mechanisms to distort and jam, and the consequences are usually grim. To avoid the inevitable, use an adjustable pedal stop and, at the fully open throttle position, synchronize the stop on the carburetor with the stop on the pedal.

11. Not having the proper size of carburetor for the application.
Having the proper venturi sizes for a given application ensures the carburetor generates sufficient air speed. Air speed creates the necessary depression (low pressure) to draw fuel through the metering systems and booster venturii into the air stream to be atomized. The Race Demon, which is equipped with removable venturi sleeves and boosters etc., overcomes most of the sizing problems.

12. Inadequate fuel cell venting.
If the fuel cell vent is too small the fuel system can malfunction. In extreme cases, inadequate ventilation can cause permanent damage to the system. As the fuel pump draws fuel from the cell it needs to be replaced by air. If the vent on the cell is too small the pump will try to draw the fuel from the cell faster than the air replaces it. This can create a vacuum in the cell, distort its shape, and starve the pump and engine of the fuel it requires.

13. Filtering of fuel cell vents.
Just as an undersized vent will adversely affect your fuel system, not having a filter on the vent will cause dirt and debris to enter it. As air replaces the fuel, the vent hose will attract anything that's in the air, including dirt, sand, or debris. These particles will eventually destroy a fuel system as well as an engine.

14. Fuel filter location.
To protect the fuel pump and carburetor, use a good filter before the pump, and filtered fittings at the carburetor.

15. Inspections.
Steel braided fittings and aluminum fittings have a life cycle. Over a period of time, the rubber bore will deteriorate causing the line either to collapse and starve the engine of fuel, or disintegrate and possibly block the passage. Radiator hoses and fan belts are routinely replaced and so, too, should fuel system components. Aluminum fittings will wear out over time and fail to seal properly. From a safety and performance standpoint regularly check the lines and fittings. Try to detect soft or weak spots by feeling the outside of the lines, and visually inspect the internals each season. Keep the connections tight.

16. Relays for electric fuel pumps
On cars equipped with electric fuel pumps, use a relay to ensure the pump is provided with the proper voltage in order to maintain proper fuel flow.

Barry Grant, Inc.


we have all seen those formulas that allow you to calculate the required carb flow rates on an engine,

CFM = engine size (cid) x maximum RPM / 3456 x VE

So, assuming 6000 RPM and 85% VE: on a 383 cid engine

383 x 6000 / 3456 x .85 = 565 CFM.

Even at 90% VE, CFM = 598

At 90% VE and 7000 RPM, CFM = 680

that indicates 650 CFM is all a stout 383 will ever need. By going to a 750cfm, you give up some better peak hp and slightly reduced throttle response due to the larger primary bores.



the formula would be just fine if the engine was 100% efficient and port flow in and out of the cylinders was at a constant air speed and the valves were not a factor, but theres a 720 degree repetitive cycle and ports generally flow only about 1/3 of that time, now divide the flow into a plenum and swap which port is running a negative vs a positive pressure about 30-60 times every second and you find true flow efficiency drops to the point where you need a good deal more potential flow capacity to match the engines requirements.
ever think of what those flow numbers mean on cylinder head flow charts, if for example the heads flow 260cfm at .600 lift and youve got 8 cylinders, it sounds like youll need almost 2100cfm of flow to keep up, but because the port only flows when the valves open and the flow rate changes with piston speed,port inertia, cam timing and exhaust scavenging,intake plenum and runner design, port reversion rates, altitude,etc. a simple formula can,t give you more than a semi-accurate guess as to the engine requirements.
the best gauge IVE found is a vacuum gauge, if your pulling more than 1 psi of vacuum at WOT your more than likely going to benefit from a larger carb or a carb spacer or a different plenum design.

viewtopic.php?f=55&t=2994

viewtopic.php?f=55&t=4362

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Re: carb tuning info and links

Postby grumpyvette » December 19th, 2010, 2:06 pm

http://www.circletrack.com/techarticles ... index.html

http://www.circletrack.com/techarticles ... index.html

http://www.circletrack.com/techarticles ... index.html

http://www.circletrack.com/enginetech/c ... index.html

http://www.circletrack.com/enginetech/c ... index.html

http://www.circletrack.com/techarticles ... index.html

http://www.circletrack.com/enginetech/c ... index.html

Here's some good reads for tuning carbs with an A/F logger:
http://www.innovatemotorsports.com/reso ... ileage.php
http://www.innovatemotorsports.com/reso ... g-hero.php
http://www.innovatemotorsports.com/resources/Stan1.php
viewtopic.php?f=55&t=6765&p=25598#p25598

Here's a quote at the Innovate Motorsports website that inspired me:
"A carbureted engine can produce just as much horsepower as a fuel-injected engine. The trick is tuning. Probably the main advantage of fuel injection is its "tune-ability." With an LM-1 air/fuel ratio meter, and a little knowledge, any carburetor is tuneable."

Other links are here at the Innovate site:
http://www.innovatemotorsports.com/reso ... entral.php

IN the VAST majority of cases a street driven car benefits more from use of VACUUM secondary throttle bores, of course knowing how to tune a carb helps a great deal


viewtopic.php?f=55&t=635

viewtopic.php?f=55&t=5229

viewtopic.php?f=55&t=1639

viewtopic.php?f=55&t=1790

viewtopic.php?f=55&t=8126
" IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
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Re: carb tuning info and links

Postby bob » April 20th, 2011, 8:14 pm

I keep coming back and reading the sub-linked info, ITS amazing what Ive over looked the first time I read through!
,information, that I caught or missed the first time by reading thru the links a second and third time!
It took me several days to read thru the linked info and threads, the first time, on carburetor tuning.
But it was NOT a waste of time by any means!
Its absolutely amazing what you can learn by doing so!
Reading thru the links in these threads is like a course in advance trouble shooting and car maintenance ,
all rolled into a self paced flow chart, based school ,where you learn what to look for.
It seems a times its an endless maze but once I started to understand much of the concepts its making more and more logical sense and its becoming easier to use the info now that I know what I'm looking for and what tools to grab to isolate and verify each system!

HERES SOMETHING THAT MIGHT BE USEFUL

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Re: carb tuning info and links

Postby grumpyvette » April 20th, 2011, 8:31 pm

if more guys did that,( took the effort too read thru the links) and if those guys reading the threads, added any info they found helpful, else ware, they find any where else it will soon prove to be extremely useful

Written by David Reher

I couldn’t tune a piano if my life depended on it, but I have tuned a few engines in my career. The process of tuning is fundamentally the same for racing engines and musical instruments. In both cases, you are making the final adjustments to a complex assembly of precision components. No one tunes a piano with a hammer, but sometimes I see racers take a sledgehammer approach to tuning engines.

How often have you seen about a racer make major changes in carburetor jetting or ignition timing? In fact, big changes in the tune-up can have severe consequences for any racing engine.

A carburetor is really an amazing device. Yes, I know that carburetors have been around forever, and that fuel injection is the wave of the future, but I’m still impressed by how well a carburetor can adapt to changing conditions. A carburetor operates on the principle of pressure differential. When the pressure in the venturi is lower than atmospheric pressure, the gasoline in the float bowl enters the airstream going into the engine. This beautifully simple system is self-compensating: when the barometric pressure or engine airflow changes, so does the fuel delivery into the engine.

You may think that the self-compensating characteristics of a carburetor are adequate only over a small range of barometric pressures. The fact is that we run the same jets in our Pro Stock engines at sea level as we do in Denver. For years I just knew that we needed to change the jetting when we went to the Mountain - until the year we tested there with our sea-level tune-up. To my surprise, the engine ran best in Denver with the same jets that we use in Gainesville and Houston. How could this be possible? Because the carburetor only reacts to pressure differential, regardless of the absolute altitude. We might change air bleeds or squirters to tune the setup to a particular track, but the jets in our Pro Stock Pontiac’s carburetors seldom change.

If you are making big changes in carburetor jetting or ignition timing as part of your tuning procedure, you are almost certainly putting your engine at risk. Virtually every high-horsepower racing engine built by a professional shop is tested and tuned on a dyno before delivery. You may discover that the dyno tune-up is not exactly right when the engine is installed in your car due to differences in the air delivery system on the dyno versus the hood scoop on the car. But after you make the necessary changes, the subsequent tuning adjustments should be very minor.

If you feel that you absolutely must tune the engine, my recommendation is to start by richening the fuel mixture or retarding the timing. For years racers have been ingrained with the idea that you have to lean out the engine and increase the ignition timing to run fast. It’s the macho thing to do: Punish the engine to make it perform. Unfortunately, that approach is dead wrong.

Think about what you are trying to accomplish when you tune an engine. The goal of internal combustion is to burn as much fuel as possible (thereby releasing maximum energy) while maintaining efficient combustion. Therefore your first step should be to richen the fuel mixture, not lean it down, to see whether the engine responds. Similarly, you want to use as little spark advance as possible because it is negative work when the piston has to push against expanding gases in the cylinder. That’s why your first step in ignition tuning should always be to retard the timing, not advance it.

If you lean the fuel mixture or advance the timing far enough to hurt performance, it’s likely that you have also damaged the engine. Detonation has dire consequences in a sophisticated, high-horsepower racing engine: You can pinch the ring grooves or knock the moly coating off the compression rings. When the flakes find their way to the piston skirts, they will eat the cylinder walls. That’s a high price to pay for an overly aggressive tuning change.

I’m often asked what an engine’s exhaust gas temperature (EGT) should be if it’s tuned properly. I don’t have the answer, because EGT is not an absolute number - it’s only a reference point. EGT readings can tell you whether you have a dead cylinder, but they can’t tell you whether the engine is tuned perfectly. EGT sensors are fragile, and their readings vary depending on how far the probe extends into the header pipe, how far the sensor is located from the exhaust port, and whether the probe has been contaminated by lead. Erroneous EGT readings can be caused by calibration errors, probe failures, bad grounds, and other faults. In short, tuning according EGT is inherently risky. Don’t trust EGT until you have established a consistent baseline for your particular engine. And don’t worry if your EGT readings are different from your buddy’s; it’s likely that your installations are different as well.

The same cautions apply to making tuning decisions based on oxygen (02) sensor readings. Oxygen sensors are designed for use with low-lead fuels, so they can be easily fouled by the leaded gas that is still used in racing.

You should be skeptical of any instrumentation when tuning. If you see a reading that doesn’t look right, it probably isn’t. Computers and data acquisition systems aren’t infallible. They only process the data they receive, and can’t discern between good and bad information. Radio frequency interference, malfunctioning sensors, poor electrical connections, voltage spikes and other external factors can produce inaccurate information. Computer programmers use shorthand to describe this phenomenon: GIGO, or “garbage in, garbage out.”

When in doubt, believe the scoreboard, not the computer screen. If you see problems in sensor readings while your car runs the same corrected e.t. and speed that it usually runs, the data is probably bogus. The most important tuning tools are common sense and a timing slip. Everything else is incidental.
" IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
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Re: carb tuning info and links

Postby grumpyvette » September 1st, 2013, 1:14 pm

heres a small tip you gain from experience, if your running a dual plane intake its got two different plenums and its not really uncommon for a carb to require the jets to be different sizes especially on the primary side of the carburetor because of the markedly different plenum volume and distance to the intake runner entrances.
look at this picture, notice the LOWER red plenum and UPPER blue plenum sections and related cylinder numbers
Image

youll notice the dual plane intake is really two distinct intakes , effectively separating the carburetor into two separate 4 cylinder configurations.
its not uncommon to find one batch or side of the intake running lean or rich, and it helps to understand that because at times youll find problems getting the engine tune correct that show indications that relate to only one plenum, but less experienced tuners fail to catch this early because its not related to only one side of the engine!


[b]WATCH VIDEOS

https://www.youtube.com/watch?v=X2W0blhIrug

https://www.youtube.com/watch?v=SQIQdsAnnA0

https://www.youtube.com/watch?v=kz7oZbtB3S8

https://www.youtube.com/watch?v=Y3hZrW4Ryo4

https://www.youtube.com/watch?v=k-Nx5HEzvlY

https://www.youtube.com/watch?v=47A6_LF295o
these pictures may be helpful
[/b]

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Re: carb tuning info and links

Postby Indycars » September 1st, 2013, 1:34 pm


Does anyone divide up the cylinder between the plenum differently or is this the standard practice?

Rick
Too much is just enough!!!

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Re: carb tuning info and links

Postby grumpyvette » September 1st, 2013, 1:41 pm

Indycars wrote:
Does anyone divide up the cylinder between the plenum differently or is this the standard practice?




most but certainly not all chevy dual plane intakes follow a similar pattern, some guys mill out the dual plenum divider wall, but this effectively converts the intake into a rather badly designed single plane, and while the extra effective plenum volume may produce better peak power its usually at the cost of low rpm fuel distribution issues

http://victorylibrary.com/mopar/intake-tech-c.htm#new

http://victorylibrary.com/mopar/no-scale-c.htm
" IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
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Re: carb tuning info and links

Postby busterrm » September 1st, 2013, 10:57 pm

grumpyvette wrote:heres a small tip you gain from experience, if your running a dual plane intake its got two different plenums and its not really uncommon for a carb to require the jets to be different sizes especially on the primary side of the carburetor because of the markedly different plenum volume and distance to the intake runner entrances.
look at this picture, notice the LOWER red plenum and UPPER blue plenum sections and related cylinder numbers
Image

youll notice the dual plane intake is really two distinct intakes , effectively separating the carburetor into two separate 4 cylinder configurations.
its not uncommon to find one batch or side of the intake running lean or rich, and it helps to understand that because at times youll find problems getting the engine tune correct that show indications that relate to only one plenum, but less experienced tuners fail to catch this early because its not related to only one side of the engine!
Hey Grumpy, by experience do you know which side will leans out or richens up? does that side need a adjustment in jet size?
Bob
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2008 Harley - Davidson Sportster 1200 Custom.
If I can't smoke the tires I want more!!!
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Re: carb tuning info and links

Postby grumpyvette » September 2nd, 2013, 9:06 am

Ive usually relied on both an INFRARED thermometer
viewtopic.php?f=44&t=579&p=19289&hilit=INFRARED#p19289
and reading spark plugs
viewtopic.php?f=70&t=202
viewtopic.php?f=70&t=3949

and use of a vacuum gauge to get a good idea on the fuel/air ratio and any changes in jetting, and power valves and accelerator pump cams required

viewtopic.php?f=55&t=1790

viewtopic.php?f=55&t=1639

viewtopic.php?f=55&t=8126

viewtopic.php?f=55&t=6765

viewtopic.php?f=55&t=1961

viewtopic.php?f=55&t=4362

viewtopic.php?f=55&t=4131

viewtopic.php?f=55&t=2773
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Re: carb tuning info and links

Postby elisalvador » July 15th, 2014, 10:26 pm

hi grumpy. I have a 72 mustang with a 302, I bought a new 750 holley and a new distributor, the issue im having is at idle engine sounds great and vac is at 19 in. I go put it in gear and the engine shuts off, I set the timing 15 deg at idle and adjusted the carburetor using a vac gauge, once the engine was running for at least 26 min,, the vac gauge needle was floating slowly from 19-17 in vac, what does this mean ??.. also again when I put the car in gear it shuts off, im kinda clueless as to whats going on ,,, need some help thanks
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Re: carb tuning info and links

Postby grumpyvette » July 16th, 2014, 10:16 am

think carefully, about the sequence of events,frequently guys apply the brake and throw the car in gear,the car stalls, so a few tests help,think logically, what changes as it goes into gear, you generally increase the load on the engine apply the brakes before placing it in gear,and may not notice changes in oil or fuel pressure or voltage which can point you to the problems source, I would plug the vacuum line going to the brake booster and try to throw the engine in gear, if it works with the line plugged your most likely dealing with a leak in the brake booster of feed line.
whats your fuel pressure? it should be set at 5-6 psi and you should check the carburetor float levels,
Id hook a multi meter to the battery, and the alternator and watch for voltage changes as the cars put in gear.
Id put the car up on sturdy jack stands and try putting it in gear, if the engine spins the rear wheels while in idle and or neutral the torque converter may be locked-up, or the clutch is not releasing, the trans may be locked up, need fluid, or the emergency brakes may be locked up on some cars,think things thru,investigate.
If the engine dies its because you had fuel , or air flow,or electric power fail or a noticeable increase in load applied
on older G.M. cars and trucks a guess is the Transmission shift solenoid is faulty. These tend to fail on the GM cars around 100K. your ford may have a similar solenoid If you can get the car to run in park and neutral, but put it into drive or reverse and it stalls without giving it gas, that what it is. The transmission torque convertor is locking up at idle speed instead of at 40mph plus putting a drag on the motor. post clear detailed pictures of the spark plugs , they tell a good deal about combustion chamber conditions, I,d also watch the vacuum gauge as you put it in gear, if the exhaust is plugged you'll see the vacuum reading drop. Id watch the voltage at the coil, if theres an ignition cut off switch you'll see voltage change as the shift in gears is made, id check the battery cables connection, loose, or corroded cables cause odd issues with the ignition, and verify your getting at least 13.5 volts at idle from the alternator and at least 10-15 psi of oil pressure because as you put the car in gear the rpms tend to drop, and if the oil pressure drops below about 5-7 psi the safety switch near the distributor cuts off the ignition voltage
" IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
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Re: carb tuning info and links

Postby elisalvador » July 16th, 2014, 10:25 am

thanks for the input ill check on that tonight , and will let u know tomorrow , thanks again
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Re: carb tuning info and links

Postby elisalvador » July 18th, 2014, 8:23 am

ok I checked out the engine , theres no vacuum leaks, I plugged up the booster , adjusted the idle screws on the carb I have 20in of vacuum , I lifted up the rear end , wheels do not turn in park nor in neutral, and the car didn't die in gear when its cold, once its warmed up and running for a while put it in gear and car dies ,,, but still with the rear wheels in the air they didn't move in park nor in neutral , now I did notice the carb did back fire through the carb , it seems like it does it when im in part throttle , or when the blades shut abruptly, now the carb is a holley 750 cfm on a almost bone stock 302 engine, (ford),
I removed the plugs and they are super black very rich, would this condition cause it to back fire through carb at part throttle ?... no it doesn't back fire at idle nor at WOT ,, only on part throttle , thanks ill post some picks when I have a chance, FYI no vac leaks were found and the spark timing is right on spot ,, thanks
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Re: carb tuning info and links

Postby grumpyvette » July 18th, 2014, 8:34 am

if the carburetor is flooding due to a defective power valve or the fuel pressure too high or a defective needle valve ,it would cause the plugs to be black and could easily cause the issues described , a simple test ,
obviously would be to test for fuel pressure, is in the 5-6 psi range

viewtopic.php?f=55&t=1639

viewtopic.php?f=55&t=1115

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set float levels are correctly,
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test the power valve,or have it replaced with a 9.5 power valve as a start point
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and replace or clean and test the needle valve and o-ring seal
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" IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
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