The Stovebolt Site Forums The Shop Area Engine Shop Engine stalls at idle when warm

I have a 55.1 Chevy 3600 with a 235 and a GM Rochester C carb. I recently installed an electric fuel pump and replaced the rotted fuel sending unit, in addition to the distributor cap, rotor & wires.

I drive it daily around town, usually less than 10 minutes at a time. Occasionally, after driving for longer periods, it will stall when coming to a stop. The starter turns it over. But, it will not hit. Eventually, it will start.

It did this today. But, would not hit. So, after getting another vehicle and a new tow strap (to replace the one that a guy "borrowed" months ago), I decided to give it another shot. It fired right up.

The fuel filter was clear with gas in it. Vacuum advance line is intact. Fuel line, pump to carb, is new rubber. I found no fuel leaks.

I'm bumfuzzled. Anyone have any ideas to troubleshoot/cure the problem?

You could try installing a Wix 33100 bypass fuel filter. I tried a one inch spacer under my Edelbrock carb with no help.Another member rec. this filter set up.It is funky but the pump -to-filter fitting is the 5/16 tip.The bypass back to the tank is the 3/8 fitting NEXT to the in inlet fitting.The single 3/8 goes to the carb.I've yet to install,but certain it will cure both our problems. Or spend more $$$ on a true regulator.

Use the electric pump for a fishing weight and go back to the mechanical pump, or install a GOOD fuel pressure regulator that can maintain a 3-4 PSI maximum pressure at all times. Your pump is overpowering the needle valve at idle and causing the engine to flood and stall. I hope you wired the electric pump with an oil pressure switch in series with it, at least.
Jerry

X2 with Jerry. There's absolutely nothing wrong with a mechanical pump on a 235 and an electric pump can cause problems. I'll bet you a cup of coffee that the issue goes away with a mechanical pump.

Ok. Gonna swap in a new mech pump & see how she does.

Stick with mechanical if you can. Keep it simple. I agree with Jerry! I have electric, not by choice.

I agree to stick with a mechanical pump, but this raises a question or more:

What is behind the engineering of the using the camshaft lobe as a means to drive the fuel pump?

When changing the characteristics of your camshaft, changing the lobe certainly changes the stroke on the mechanical fuel pump thus changing the way the fuel pump acts. Are there any instances, where someone has modified the Fuel pump lever to their camshaft duration?

The fuel pump lobe is shaped exactly the same regardless of how radical the intake and exhaust lobes happen to be. There are 13 lobes and a distributor drive gear on a stovebolt cam- - -12 for the valves, one for the fuel pump. Why would anyone want to tinker with a pump lever?
Jerry

Good question Jerry. There's a finite amount of travel to play with. Maybe one could get a tiny bit more fuel or fuel pressure by playing with the lobe but would it gain any measurable performance. Beats me.

The mechanical fuel pump is driven by the camshaft lobe because the engineers wished volume, and to some extent pressure, to be keyed to the fuel demands of the engine. Engine RPM increases, fuel demand increases, fuel pump works faster and delivers more.

Since an electric pump will deliver maximum pressure and maximum flow at idle, aftermarket electric pumps often create problems if the enthusiast does not consider this issue.

Jon.

It appears the questioner above assumed that one of the valve lifting lobes also operated the fuel pump. That's not the case, as that would probably cause premature wear on a single lobe, making it do double duty.
Jerry

Well, I swapped in a new mech pump. But, when I tried to start, it wouldn't hit. Then, I lost all power. Got my test light and found the pos cable was not good. Swapped in a new cable & it fired first lick.

All is well. Thanks to everyone!