car falls flat in third gear



car falls flat in third gear

Postby grumpyvette » June 18th, 2013, 11:18 am

POSTED BY PRO67CHEVY
"Hey All. Trying to get the chevelle ready for its debut trip to the drags. After playing on some back roads to see how the car handles, I found a severe bog after standing on the pedal for a few seconds.

Car info: 468 BBC with small solid roller, cast oval ports, performer RPM, and a 950 HP carb. TH400 w/ standard pattern, 12 bolt with 4.10s

Fuel system: Mallory Comp 140 pump and filter, return style regulator with 3/8" feed, and 1/2" return.

Dropped it into 1st, take it almost 6k, shift into 2nd, take that to about 6k, then I hit 3rd and a second later the car loses all power and nose dives down. I let off and it drives normal again.

I'm sure it's fuel. But where. I can't imagine the pressure needs to go up. It’s at 7psi now. I have a 3/8s feed line and a 1/2" return line. Don't know if the difference in line size affects anything. There's also a vacuum port on the regulator that I believe increases pressure at WOT, it's capped off but not sure if that is worth looking into. I don't think the pump is running dry but I did only have a 1/4 tank of gas. Carb issues? PV not working?

Thanks for Looking!"


thats a classic symptom of the carbs fuel bowls running dry because the fuel supply is not consistent.
this is far more frequent with the dead head fuel pressure regulators OR when guys place the return style regulator before the carbs inlet port.
obviously your fuel filter(s) and fuel line internal size and fuel pump volume and pressure, have an effect your results
Id suggest at least temporarily connecting a fuel pressure gauge at the carbs fuel inlet port so you can monitor the fuel pressure at that point during a race.
if the pressure falls at the carbs inlet port its a supply issue, if its consistent I,d be looking at a blockage in the fuel inlet ,especially if its got a brass in carb filter.
[b]you might be amazed at what a few tests with a fuel pressure gauge can tell you

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IF YOUR CURRENT FUEL PUMPS CORRECTLY SET UP AND FUNCTIONING, you should not have any problem, but a partly clogged fuel filter might also be a problem.
the fuel pressure gauge at the carbs inlet port should let you know what to look for.
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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first step is always to verify both fuel bowls have the floats correctly set (EASY ON MOST HOLLEY CARBS WITH A SITE PLUG)
[/b]

these brass inlet filters need to be replaced occasionally as they tend to restrict fuel flow
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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Re: car falls flat in third gear

Postby grumpyvette » June 23rd, 2013, 2:32 pm

Frank came by with one of his friends to have me look at his 1970 dodge polara, its a rather heavy car, but he has a high compression 440 and a 3.54:1 rear gear and a trans with a 3200 rpm stall converter , hes got a hydraulic lifter performance cam, and a high rise dual plane intake, headers and a few other mods. the problem, he was having an issues similar to the other listed above in that he had a engine that seemed to run out of guts in high speed passing. AMAZINGLY HE HAD NEVER TESTED , the fuel pressure and when we did we quickly found the pressure dropped of to less than 2 psi at the carb inlet on a prolonged wide open throttle pass.
the factory fuel lines looked to be about 3/8' metal , I suggested replacing the fuel filter and the fuel pump, which we did and it helped a good deal, but its obvious looking at the test gauge that upgrading to a true 1/2" fuel line system with a return style regulator would be the, ideal, as the car originally came from the factory with a 383 dodge, not the larger 440 which he built and installed later.
the original engine made about 330 hp, the current engines easily making 430 hp or more, and while the car more than likely weighs in the 3800 lb range its certainly fairly quick, or at least noticeably faster that its outward appearance would suggest.
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Edelbrock 7194 - Edelbrock Performer RPM Camshaft Kits Details

Chrysler

Operating Range 1500-6500 RPM
Duration Advertised 300° Intake/308° Exhaust
Duration @ .050'' 238° Intake/246° Exhaust
Lift @ Valve .480'' Intake/.495'' Exhaust
Lift @ Cam .320'' Intake/.330'' Exhaust
Lobe Separation Angle 110°
Intake Centerline 105°
Intake Timing @ .050" Open 14° BTDC
Close 44° ABDC
Exhaust Timing @ .050" Open 58° BBDC
Close 8° ATDC

BTW he had one of these potential fire hazards in the fuel line just before the carb feed port
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simply replacing it with a section of fuel line allowed the fuel pressure to jump to almost 2.75psi at the carb inlet vs the barely 2 psi with it in place so it was either clogged or very restrictive.


btw , testing showed the fuel pump was also rather marginal as it maxed out at 5 psi ,
I strongly suggested he upgrade to a good performance fuel pump and AN #6 lines at a MINIMUM, if it was a race car ID suggest no less than 1/2" or AN#8
I,t amazing the number Of guys I see who not only fail to test the fuel pressure and volume but check to verify the lines and fuel filter are not restricting flow.

a mechanical pump, on a stock V8 engine should produce a solid supply of fuel, a minimum of 7 psi pressure reaching the carb inlet and fuel pressure regulator area and adjusted to as steady 5 psi, flow at least 1 quart each 30 seconds, and ideally use a return style regulator, a reasonable fuel line size and a decent fuel filter
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IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!
grumpyvette

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Site Admin
 
Posts: 14105
Joined: September 14th, 2008, 1:40 pm
Location: florida


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