Vapor Lock issue?

Recently purchased 85 C10 and been having issues after driving for about 10-15 miles. Once at cruising speed the engine seems to slightly rev itself as well at one point stalled on me after sitting in traffic for some time. Also live in Phoenix so it has been warm. Vapor Lock issue? Any suggestions how to solve or could it be possibly be something else. Only happens after driving for awhile so lead me to believe the engine compartment was heating up and causing vapor lock.

GM has 2 and 3 port fuel pumps for the 350, and some folks make the mistake of using the 2 pump (no return line to the tank) when they should use a 3 port. The 3 port allows fuel to return to the tank and helps keep it cooler, instead of dead-heading it in the hot engine compartment between the pump and carburetor when the float shuts off flow.

Bruce

i think my 454 has issues with vapor lock as well.

after driving a similar amount of miles if i sit at like a drive through or in traffic or like the other day i put gas in the truck then when i went to leave the truck died and didnt want to start back up. got it started though and got it home. doesnt seem to be an issue for me if im moving. though i have not tested this much.

my 454 has the 3 port fuel pump so i cant say for sure if it will solve the problem. but hell its possible my fuel pump is going out again i havnt tested much.

one thing to check is when the truck does die pop the hood and see if there is any fuel in your fuel filter. the first time this happened to me i had no fuel in the filter. buddy drug my truck home and let it sit over night. the next morning there was fuel in the filter and truck started right up. i suspect that if i would have just waited long enough it would have cooled off and been fine for a little while longer.

75gmck25 said:

GM has 2 and 3 port fuel pumps for the 350, and some folks make the mistake of using the 2 pump (no return line to the tank) when they should use a 3 port. The 3 port allows fuel to return to the tank and helps keep it cooler, instead of dead-heading it in the hot engine compartment between the pump and carburetor when the float shuts off flow.

Bruce

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The 3 port helps between the pump and the tank but it still doesn't solve the heat issue between the pump and the carb. It still dead ends at the carb.
I wonder if you could disconnect and cap the return outlet on the pump. Then install a tee connection at the carb inlet so you can run the return from there back to the actual return line to the tank?????
That would keep the fluid constantly moving between the pump and the carb instead of dead ending it at the carb.
Maybe you would need a three port pressure regulator at the carb?????
IDK...just thinking out loud.

Mine has the metal line from pump run in front of block up to intake then rubber line to carb. I put pipe insulation from pump to top of intake on metal line in hopes to eliminate vapor lock. So far, 4 years and no vapor lock at all and it didn't do that before since purchase in 2015. You can get insulation at hardware store.

Thanks for the responses. I am actually thinking the engine reving/lunging on its own and the stalling are non related issues. I relocated and replaced the fuel filter and haven't had the stalling issue since but once engine heats up and in 4th gear it lunges forward. Someone suggested it could be related to transmission. Truck has a 4 speed 700R4. Any additional thoughts??

Backfoot100 said:

The 3 port helps between the pump and the tank but it still doesn't solve the heat issue between the pump and the carb. It still dead ends at the carb.
I wonder if you could disconnect and cap the return outlet on the pump. Then install a tee connection at the carb inlet so you can run the return from there back to the actual return line to the tank?????
That would keep the fluid constantly moving between the pump and the carb instead of dead ending it at the carb.
Maybe you would need a three port pressure regulator at the carb?????
IDK...just thinking out loud.

Click to expand...

i think you can do this (may have to switch to a 2 port pump though). But again, we'll have to wait until the weekend until i can really get into this.....if at all. Just too busy.

i think the stock steel factory line behind the alternator and in front of the engine works ok at keeping the heat out though.

My 69 will boil the fuel in the carb if I have to let it sit and idle a long time. Only happens after I shut it off. I am going to try some fuel that doesn't have ethanol in it to see if the boiling point is raised enough to not be a problem. It gets hot enough that the pressure in the float bowl pushes fuel through the venturi and floods the intake. I can see it leaking out the sides on the butterfly pivot rod. Really sucks if you just need to shut it off and run in somewhere and go back out to leave. Foot the floor when cranking sometimes clears it out. Seems alright as long as it's running and the gas doesn't get a chance to just sit in the heat.

If you are having issues like this a lot of people call it percolation. You know like making coffee. A bit of googling will give you some suggestions like a 3 port filter that has the provision for a return line to the tank and phenolic spacers for the carb to get it off the heater beneath.