ok heres the deal, my car is having fuel issues when its hot. I thought it was vapor lock at first, but i have done everything to avoid that. heres what its doing, when it is cold the cars a low 13 second car, but whenever i drive it for a while and it stays at its operating temperature (160*-180*) for a while it starves itself for gas and misses (i can see it in the fuel filter). heres all i have done to try to solve the problem.

I have switched intakes

switched carbs

ran new aluminum 3/8 line from the tank up

put a heat shield over my fuel line

installed a 8 psi electric fuel pump (right after the line that comes out of the tank) with a regulator, and removed the 7 psi mechanical i had

and my most recent is that i rerouted my fuel line to the innerfender well away from exhaust heat, i can put my hand over it where it passes the y pipe and its maybe 90-100* there

and it still does it

the only thing i havent done is the tank and the pickup from the tank, along with the rusty line coming from the pickup

also, i have some of the lines from the tank blocked, with the exception of the original vaccume one that has that canister attached, the other ones that were plugged, is the return and the ones that went to the carbon canister.

any input is appreciated, especially further expansion of what all the lines from the tank do and what you guys can see cause this?

Thanks Russell

 

You don't have the tank vented. As gas is removed, it creates a vacuum so the pump can't pull any more out of the tank. After it's been sitting, small leaks allow it to equalize so it can pull gas out again.

 

I have tried it with the cap off, it didnt help any, would that work as a vent

 

Well, you didn't mention that.

You need to put a fuel pressure gage on it that you can monitor while driving. Don't run a line with gasoline in it inside the car, the common approach is to tape a gage temporarily to the outside of the windshield so you can watch it.

I would say you need to drop the tank and look at the pieces that you haven't replaced, but if it truly runs fine when cold, that doesn't sound likely. At any rate, monitor the fuel pressure so you know for sure what's going on.

 

yeah thats probably what ill do next, i would say ill have to pull the tank eventually

I just thought of something else, the fuel line runs overtop the trans, is it possible for the trans to heat up enough to cause a vaporlock (I know its a far stretch because exhaust temps a 500*plus and if a trans is over 200 it wont shift, but i am at a loss)
thanks 5 7
Russell

 

ok, i got a gauge and put it right before the carb, no matter where i put the regulator, it stays at 5 psi and if you rev it it drops to 4, also theres air in the fuel filter at this 5 psi, could there be a pinhole maybe in the rusty line coming from the sending unit or something?
Russell

 

Are you sure you running out of fuel in the bowl? what type of distributor? icm starting to get heat soaked/ coil maybe?

 

i have a mallory unilite distributor, with a msd blastor 2 coil, i know its not them both are new. it has to be somewhere in the fuel deliver, btw i have yet to warm it up enough with the gage on it to see where it is, that was just when it was cold, i have finals next week, so time is at a minimum for a week
Thanks
Russell

 

Ok i think its a pinhole in the line coming from the sending unit, im gonna drop the tank and see friday, anyone know where i can get a sending unit relatively cheap? thanks
Russell

 

before you go any further with it. i'd check some basics. check fuel volume at the carb. pull the hose off it, let it go into cup should be, between a pint and a quart in 15seconds of being on. you might have a crimp.

 

the crimp is a good posibility, i have put all new line on though, except for the sending unit, so if it was a crimp, the new line should of changed that. and my last final is tomarrow so ill finally have time to mess with it
Russell

 

If you are sucking air in to the fuel line then I would think it shouldn't matter whether the engine is cold or not. Is there any correlation with the fuel level in the tank? I wonder if you have a hole in the pickup tube that sucks air once the fuel drops below the hole.

 

Air in the fuel line will act like air in the coolant system. Put a purge valve at the highest point in the fuel.
If you're talking about a pin hole on the pickup line to which the sending unit is mounted on, why don't you just clamp a piece of fuel hose over the pin hole, but be sure to place the clamp directly over the hole. No sense in spending money on the sending unit if it isn't the problem.

Heat soak is the reason the fuel pump is placed in the tank so that the fuel will will keep the pump cooled.