a weird frustrating fuel problem

[darken7]

I have a problem. I recently acquired a 71 F250, and I have slowly been replacing parts and tuning up the engine. For some reason when the engine gets up to operating temperature, the carburetor starts to experience problems. By problems I mean the fuel pressurizes at the inlet, and the bowl empties. I removed the air horn with it running while this was happening and tapped the float. This released an large amount of pressure through the needle, almost like the psi on the pump was too much. I replaced the fuel pump, still have the problem. I replaced all of the filters in the fuel line, still have the problem. Changed the thermostat to a lower temp, still have the problem. Rebuilt the carburetor, still have the problem. Rebuilt a different carburetor and swapped them, still have the problem. Before anyone suggests setting the float and fine tuning the carb, trust me I have spent ample time doing this and know that I have it right. When the truck first reaches the operating temperature, it runs like a dream. When it has been there for a little while the problem arises. I have even went so far as to replace the spark plug wires, dist. cap, and everything else I could think of to no avail. A friend of mine suggested vaporlock, but I don't think it is that. Please Help. if there is any other information needed that would help diagnosis please let me know. I apologize for the lengthy post, but I feel it is necessary to cover all the bases. Thanks.

[peanutman]

d7 i am by no means a expert but you ask. First to dispell the vapor lock try running a rubber fuel line from your fuel pump to your carb without any filters. Rubber should not vapor lock but i don't recommend leaving it there permanently-just to test it.
Do you maybe have an inline filter on backwards. Have you checked the full run of the fuel line from tank to carb.
Did you replace the timing chain and maybe not put the pin back in the ecentric causing it to slip and not powering the fuel pump at all times. Have you checked the fuel pump pressure per the manual even though it's a new one this may pinpoint a problem somewhere else. Has to be the line, a filter, the pump, or the carb. Maybe vapor lock.
I don't know enough about engines but could it be a engine breathing problem. Someone here should be able to help you.
But what you described it sounds like the float is sticking

[FORDification]

This kind of problem can often be remedied by isolating the carburetor from the engine heat with the use of a phenolic carb spacer.

[Jake11]

What do you mean by "bowl empties"? The fuel leaks out of the float bowl? Or is it overflowing out the carb?
Does it quit running, or stall? Jake

[willowbilly3]

What engine/carb?
I had a somewhat similar problem with heatsoak on my 72 with the 300-6. I think the fuel in the line pressurized from vaporizing. After a short heat soak it would then run out the gas in the carb and die and not restart. If I cracked the line and let the pressure off it would start right up and be fine after that. I remedied the problem with a fuel pressure regulator. Set at around 1 1/2-3 psi.
The stock carb on my 390 would percolate the gas out and flood the engine on heat soak (10-15 minutes setting after being run). I tried everything, different spacer, heated spacer, heat disconnected. I finally got tired of fighting it and put a 350 Holley on and ended that problem. I had a 68 with a 360 that had a heat soak vapor lock problem too, sold that one before I ever got it fixed.

[wildcard]

Like peanutman, I'm no expert. My experience has been that Keith is the man to listen to. Just gonna throw another idea out there though.
The PO of mine had replaced the fuel pump with an inline electric pump. On the way down they had about the same problem as yours. Ended up bringing it the rest of the way on a trailer and lowering the price after replacing a bunch of parts still having probs. To make a long story short, he had put on a pump for a fuel injected engine. Way too much pressure. And I got a good deal on a truck with lots of new parts I didn't have to wonder if they were going to need replacing soon. Just my Good luck.

[darken7]

oh I forgot to ask for suggestions on a regulator or a spacer.

Thanks

[FORDification]

http://marine-performance-parts.com/1ta ... y2bbl.aspx

One thing I forgot to ask....does your carb have an aluminum spacer under it with a heater hose connected to either end of it? If so, you might be able to at least minimize the problem by bypassing that spacer altogether. That was something added by the factory to aid in warm-up times and to keep the carb from icing up.

[willowbilly3]

Keith, thanks for that link, I had a hard time finding one for a 2 bbl. when I needed one. The Holley was the fix for me, I found a barely used one off the HAMB for $75 On the MC the float bowl is more exposed to the engine heat and therefore prone to heat soak and percolation. The Holley has the fuel bowl up away from the heat.
Also if you have the efe butterfly in the exhaust manifold, make sure it is opening.

[DuckRyder]

A 71 should have a pressure cap and a vent to the charcol canister. Make sure that if someone has plugged the vent lines it has a vented cap...

[fordman]

excuse me because i have been gone a while and have forgotten lots of little things. but if your wanting to plug off a fitting in the intake. wouldnt a pipe plug be what your looking for? that is if you are looking to remove a water source from the carb spacer plate. if you have just a vacuum hose going to the spacer plate then stick a bolt in the hose when you remove it from the spacer plate.

[FORDification]

You can just bypass that heated spacer by removing the hose from the front of the spacer and then removing the hose from the back of the spacer, and essentially inserting a connector between the two. However, since the two ends obviously wouldn't reach each other, a single longer piece of hose from the intake manifold nipple back to the heater core nipple would quickly solve that problem.

[darken7]

Thanks, is it alright to just leave the openings on the spacer open? Or do I need to cap them? I will update after I get a chance to work on it again.

Darken7

[DuckRyder]

You can leave the openings in the spacer open...

It has been quite some time since mine had that set up, but I thought mine had a twin outlet on the manifold and a "T" fitting in one of the heater hoses.

[willowbilly3]

You can just leave the coolant passages on the spacer open.