ever wonder whats inside a manual fuel pump



ever wonder whats inside a manual fuel pump

Postby grumpyvette » August 30th, 2011, 9:50 am

heres a carter muscle car pump,thats been taken apart, notice the two small one way valves, So how does a chevy manual fuel pump limit fuel pressure, the diaphragm moving on the fuel pump lever, moves first down, to create a slightly lower pressure to draw in fuel,to a limited enclosed area, then upward due to the force of the internal spring ,that forces, the fuel momentarily trapped above the diaphragm out thru the other one way valve, the amount and pressure is determined by the pressure return spring ,in this pump design, a known, and pre-determined, load rate or spring load resistance, ITS NOT a direct mechanical leverage, that compresses the fuel,its spring pressure on the diaphragm and one way flow valves cause it to flow, but keep in mind rapid changes in the engine rpm are known to cause pressure spikes, or drops in volume, in some cases,as the area over the pump diaphragm moving on the fuel pump lever and valve sizes, at high rpms theres frequently not enough time for the spring under the diaphragm to maintain the required pressure long enough too fully drain the area, before its forced open again, so the increased number of pump strokes effectively limit the movement of the diaphragm to a lesser distance because the fuel return spring and valve don,t have time to fully empty the area area over the pump diaphragm to fully empty that area, so the pressure and flow remain fairly consistent.
how does a chevy manual fuel pump limit fuel pressure, at low speeds the diaphragm spring gets a full stroke and return, at higher speeds its limited in the time its allowed but the spring pressure returning the diaphragm is the same, thus pressure remains somewhat consistent as does volume , due to a higher number of lower volume pulses exiting the pump.
IF you really want consistent pressure at the carburetor inlet port youll want a return style fuel pressure regulator.
AGAIN PRESSURE AND FLOW RATE ARE TOTALLY DIFFERENT FACTORS

the normal manual fuel pump supplys a fuel pressure at the carb inlet port that can and probably does vary from 6-8 psi, the carbs needle valve will allow fuel to flow into the fuel bowl when the fuel level drops enough to allow the needle valve too open, the potential flow volume has little effect on the carb AS LONG AS ITS SUFFICIENT to keep up with demand and supply the carb with more than enough fuel to allow the floats to shut the needle valve when the carbs fuel bowls fill, having a surplus potential flow volume hurts nothing as long as the pressure can,t over come the floats weight ant push open the needle valve, having LESS than the required flow volume when the fuel bowl float is allowing the needle valve too fully open results in a lean miss fire at higher rpms
yes there ARE some aftermarket manual fuel pumps that produce 15 psi that will flood a carb, without a fuel pressure regulator with a return line design, in use.
WATCH VIDEO
https://www.youtube.com/watch?v=pdwD42c1JDE
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http://www.aa1car.com/library/fuel_pump_mechanical.htm
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this Holley pump, pictured below is similar but it has a larger diaphragm and twin valves , that allow more fuel to exit the pump effectively increasing flow, so in many cases a bye-pass fuel pressure regulator is required to maintain steady consistent fuel pressure
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the stock steel fuel pump push rods are heavy and under higher rpms tend to wear the cam lobe and bounce causing fuel delivery issues as the inertial weight over comes the pumps return spring, at higher rpms.keep in mind the fuel pressure is determined by the springs resistance
bronze tip fuel pump push rods in my experience tend to flare or rivet on the tip ,expending over time making removal very difficult, a roller tip rod in theory has advantages, of low friction
or if you want to keep cost a bit lower go carbon fiber, low friction and much lower weight., and reasonable cost, all advantages

fuel pressure and fuel flow volume are two totally different factors
the needle/seat, in a carbs float bowl,controls the fuel level by opening and closing the needle valve, in the fuel bowl, and its designed to and generally can control fuel inlet pressures below 8 psi, the manual fuel pumps designed to supply a constant 6-8 psi in most cases
(but generally works best at 5-6 psi)volume of flow only come into play once the needle valve opens and that relates to how quickly the floats being raised back to the point the needle seat closes
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YOU GENERALLY SET THE FLOATS TO JUST LET FUEL WET THE SITE PLUGS LOWER THREADS, BY ADJUSTING THE NEEDLE SEAT HEIGHT IN THE FLOAT BOWL
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AGAIN PRESSURE AND FLOW RATE ARE TOTALLY DIFFERENT FACTORS

the normal manual fuel pump supplys a fuel pressure at the carb inlet port that can and probably does vary from 6-8 psi, the carbs needle valve will allow fuel to flow into the fuel bowl when the fuel level drops enough to allow the needle valve too open, the potential flow volume has little effect on the carb AS LONG AS ITS SUFFICIENT to keep up with demand and supply the carb with more than enough fuel to allow the floats to shut the needle valve when the carbs fuel bowls fill, having a surplus potential flow volume hurts nothing as long as the pressure can,t over come the floats weight ant push open the needle valve, having LESS than the required flow volume when the fuel bowl float is allowing the needle valve too fully open results in a lean miss fire at higher rpms
yes there ARE some aftermarket manual fuel pumps that produce 15 psi that will flood a carb, without a fuel pressure regulator with a return line design, in use.
theres also light weight carbon fiber push rods
http://www.summitracing.com/parts/hrs-94475/overview/
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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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