Help! Very hard to crank after hot!

[jckkys]

The terms you use are confusing. Cranking is what the starter motor does. It will "crank" whether or not the engine ever starts. The engine fires or starts, while cranking, when there is a spark and a combustible fuel/air mixture delivered to the cylinders. The U tube video shows a mechanical fuel pump with a perforated diaphragm and good seal on the internal shaft. This pushes the fuel from this perforation out of the vent hole. Fuel is still being pumped to the carburetor.
Heat soak of the engine, after being shut down, boils or percolates the fuel in the float bowl. This vaporized fuel fills the intake displacing the air/oxygen and delivering a mixture too rich to burn. Pumping the accelerator only further "floods" the engine not allowing it to start. To start a hot engine that's flooded just push the accelerator about 1/4 of a stroke and HOLD the pedal there. Now crank the engine to flush the excess fuel out. With air/oxygen in sufficient proportion to the fuel vapor, the cylinders will fire ie. the engine will start. There's no reason to diagnose this as a fuel pump problem. The owners manual of any carbureted vehicle describes the hot restart procedure.

 

[TJ.Harry]

Right. I've tried the 1/4 push of the pedal with no luck. Only 'starts' with pumping of the pedal.

 

[Apogee]

I run a phenolic spacer between my intake and carb as a thermal barrier between the two...it definitely helped my hot starts.

 

[TJ.Harry]

I think I had heard of that before. Any link to one that fits a 302 with a 2 barrel?

 

[JWMcCrary]

The terms you use are confusing.

Not when you are from Alabama and Mississippi

 

[Timmy390]

Verify your tank is venting properly. I chased this issue for a long time on my big block Mach 1. Turned out the combination of heat and suction from the tank not venting was pulling fuel back into the tank emptying the fuel line. Adding a phenolic spacer between my intake and carb helped in limiting carb bowl boil off but the issue was still a problem until I got the tank venting correctly.

No hot starts problems since.....

Tim

 

[TJ.Harry]

Hmm. Could be a good point. I know my tank doesn't vent great since if I go wide open with the gas pump air can't escape fast enough and gas comes back through and out the filler neck. I just make sure to go slow with the gas pump. How did you solve your issue?

 

[Timmy390]

On the Mach 1, the vent is a notch in the filler neck end where the gas cap seals. I filed the notch more/deeper so it would work with the new seal I installed in the cap. The cap on the Mach 1 is an assembly more than a cap.

For the Bronco, you need a "vented" cap (or some other device) that lets air in. As you drive and take fuel out, air has to be let back in or it creates a suction that will pull fuel back out of the lines once you stop. It will also make the pump work harder than it needs to.

Not saying that's the issue just passing on my experience with the symptoms.

Tim

 

[TJ.Harry]

Hmm. I believe I'm still using the stock cap. Not sure if it's vented or not. It still has the vapor lines to the canister though. Shouldn't that allow proper venting? I guess a new vented cap couldn't hurt.

 

[jckkys]

If the long established method for restarting a hot engine after a period of heat soak doesn't work, another diagnoses is in order. Try pulling the top cover off the 2100 when this problem comes up. See if there's any fuel in the float bowl. If it has boiled out the accelerator pump does nothing. If there is even a little fuel in the bowl it should squirt out of the nozzles with even a slight movement of the throttle. That would be more than enough to start a hot engine. If there is no fuel in the bowl, have someone crank the the engine while you watch for fuel entering the bowl through the needle valve. I use the word "crank", as defined in English, as the starter motor turning the crank shaft. Until there is fuel in the bowl, pumping the pedal, again, does nothing. If and when there is fuel in the bowl and the accelerator pump functions, pumping the pedal floods the engine. It's never a good idea with a hot engine. If cranking doesn't put fuel in the float bowl, you have fuel delivery problem. That could be vapor lock. A bad pump would kill the engine while cruising or accelerating when the engine needs fuel.

 

[jw0747]

When the engine is hot and won't start pump the gas pedal 3-4 times then hold it all the way down to the floor and crank the engine. This method always worked for me when mine had a carb.

 

[blubuckaroo]

Out of the owners manual...

This method can be used with aftermarket carbs as well.