Vapor Lock?

[BBM3]

I have a 1975 K10

Today I had a problem with fuel delivery.
Ambiant temperature is about 70F. The warmest day I have driven my truck since I bought it.
After driving about 10 miles I began loosing power under load. I pulled over looked at the new plastic see-through fuel filter I installed near the carb and could see that rather than being full of fuel, fuel was surging into the mostly empty filter.
The truck started and idled fine but was clearly not getting enough fuel to the carb under load.

I loosened the gas cap. No whoosh of air and I tried driving off without the gas cap just to be sure it wasn't a vent problem.
No joy.

I recently installed a dual exhaust system and took care to make sure there is at least a couple inches of clearance between the exhaust and fuel lines. There is one place where the fuel line is 2 inches from the right head pipe which is about the same as the original was.

Maybe the fuel pump? It looks new.
Insulate the fuel lines?
Wrap the righthand head pipe?

Thanks for any suggestions.

-BB

[Irish_Alley]

think vapor lock is more for "hot starts" the fuel filter might not be filling up due to the engine not running right

[BBM3]

I think the engine is running fine. Water temp was about 180F driving and was about 200F after parked.
It has always run fine in cooler weather and ran okay today until I stopped and let it sit for about 15 minutes.
After my 15 minute stop It started, idled, and ran well for about a mile before I lost power / fuel.

[BBM3]

Maybe vapor lock is not the right term. Regardless, the fuel was boiling (vaporizing) but rather than in the float bowls which normally leads to hard hot starting after a heat soak cycle, I believe my fuel was vaporizing in the fuel line before the fuel pump.
I made a heat shield today between the right head pipe and the fuel line.
It seems to have worked. I drove the truck hard, parked it for about 15 minutes, took it back out for another flogging and no more problems.
The true test will come once the temperatures get into the high 70's - 80's.


If this works I'll make a more robust version.