Is this fuel vaporisation

[Lippyp]

I was driving around town today running some errands and my truck started to cough and splutter when pulling away from idle, no power initially, then once I was up and moving seemed to be all right, even when accelerating. When I eventually got home I looked under the bonnet and there seems to be a significant amount of air/fuel vapour in the top of the fuel filter just before the carb. I am assuming that this shouldn't be there and that I am suffering from fuel vapourisation. Is this the likely cause of my problem?

I am running standard manifolds not headers, with a Carter electric fuel pump on the frame rail. Most of the driving today was low speed around town with quite a bit of stopping and starting, truck didn't seem to get too hot.

Any suggestions for a cure? I need to replace the fuel lines soon as they are starting to look a little crazed so what would be best to replace them with and any tips on where to run them? Could this be electrical rather than fuel related?

[Gordo]

You may want to check your accelerator pump in the carb before you dig deeper. With engine off, remove air filter assembly, climb in and look down the primaries with a flashlight, then manually open throttle linkage to wide open throttle slowly, you should see a equal squirt of fuel entering each primary throat. Don't worry about the air pocket in the filter, that's normal. If that looks okay another possiblity would be the vaccum advance diaphram is shot.

[ebfabman]

Your fuel supply line may not be sealed and could be sucking air by the fuel pump. Also ckeck to see that you have 7-10 lbs of fuel pressure at the carb.

[Lippyp]

The carb is only two years old with about 5K miles on it so unlikely to be bad, but I'll have a look down the top. I'll also check that all the connections on the fuel hoses are tight. When I say an air pocket, I mean about the top third of the filter is air. If there is no squirt of fuel does this mean a carb rebuild is neccesary?

When you say the vacuum advance diaphragm is this in the distributor, the previous owner fitted a Mallory Twin point distributor which has given me some grief in the past, time for HEI?

Any further suggestions welcomed.

[tom hand]

Also check the mechanical advance in the distributor, if the weights are stuck it will run as distribed. And do the basics, dwell, timing, etc.

[Lippyp]

I've just had a thought, this happened the first drive after I fitted my new K&N air filter, I wonder if I've knocked the vacuum pipe for the advance loose. Kinda dark outside now as it's gone 10pm here, guess I'll have to wait until tomorrow to check. Keep the suggestions coming.

[Lippyp]

Climbed in, checked the carb, two good squirts of fuel down the primaries when throttle is opened. Whilst doing this I noticed that the little rubber nipple plugging the unused timed vacuum port connection on the carb had split, quick trip up the road to my little local car spares shop (would you believe it, rural Lancashire UK,and the owner has just bought a 70's Mach 1 Mustang!) bought a "diesel fuel injection bleed screw cover" (little rubber cap!) for the grand sum of 40p ($0.63) bunged it on and she runs and idles better than she has for quite a while, must have been leaking for some time.

Thanks to all for their suggestions particularly about the vacuum advance. Gotta say I was expecting a much more expensive fix!