Topic: 78 Formula Vapor Lock??

[Shanec1226]

Hi I have a 1978 pontiac formula, when I received the car the fuel line from the fuel pump to the carb was badly bent. So, i ordered a new one that was wrong and I just used some rubber fuel line instead and put an inline fuel filter. The car did not run before this so I do not know if this is the problem but when I drive it for more than 10-15 minutes the car starts to buck and stall. Will not start again for a while, if i pour cold water onto the line it takes less time to be able to start again so I believe the issue is vapor lock. Could the ∏bber line be trapping too much heat compared to the OEM metal line or is it the inline fuel filter. I explained this to a worker at a local hot rod shop in Las Vegas and he said it could be the fuel pump even though I replaced it with a new one that is OEM. Thanks in advance.

[Wallington]

Not the hose, around half of these cars have hose fitted there, shouldn't, but do, without problems. As long as it is good quality fuel hose and not thin-walled vacuum hose or similar. Does it have headers? Take the filter off and test. Does it have the correct fuel cap that is open to breathe and return line hooked up?

[Shanec1226]

It has the original headers. The filter is fine. and the original fuel cap was cracked so i grabbed one from auto zone i believe... Should I buy a new one and see if that could be it? and the fuel return line seems to be fine also

[Stringer]

This may seem crazy but does it still have a catalytic convert? It could be plugged up. I had the same thing happening to my 79 TA last summer (I live in Phoenix). I tried everything thinking it was vapor lock. Then one day it got so bad, it stalled out and would barley run when started.

Frustrated, I took it to a shop. They were quite certain it was a plugged cat.  I brought it home, cut the cat out of the exhaust, and sure enough I couldn't even see light through it.

I haven't had a problem since.

[FULZGOLD]

For what it's worth, I had some issues on an old Mustang that I had many years ago. Ran fine when cold, but after it got warm, mis-fires and rough running, no power at all. First thoughs took me through all the fuel system components. No luck. Turned out it was the plug wires. When some of them got hot, they broke down and gave me a fit. Replaced. Cured.

So, it might not always be what you're thinking... check everything.

[ta78w72]

The hose from the pump to the carb is under pressure.  This makes a vapor lock in that area harder to occur.  The line from the tank to the pump is under low pressure as the pump draws a vacuum to pump the fuel.  Your vapor lock is most likely in that line because at lower pressure the fuel will turn to vapor at a lower temperature.