Fuel Problem. Vapor Lock??

[x-unimog404]

Trying to diagnose a possible fuel problem on my 73 FJ-40.
I have stock f-engine, carb,intake, and a header.
Fuel system is stock, with the emmision control canister, lines and vacumn switch in place.
Problem.
After a 30 minute cruise to test out everything, (just got back on road after frame off), engine was running good.Outside temp about 75.Temp was normal, lacked a little punch on accelleration, (timing).fixable.
Stopped for a few minutes in a shopping center, shut off engine for abou ten minutes. Started back up and was cruising through parking lot.
Engine just died. Could not fire up. Smelled like gas, kike the carb had flooded.
On a quess, I checked the fuel tank, it was reaaly pressurized, opened the gas cap and a rush of fumes came out.Checked eveything else out, no leaks or anything noticeable.
After about ten minutes, tried to start it up, it started with a few clouds of smoke, ran for a few minutes, then quit. tried again and it started, and stayed running.
On the trip home, only a couple miles from home, at a stop light, it died again.
Pushed it to the side of the road and tried to start. No good, opened the gas cap, nothing this time.
After repeated tries to start, and letting it sit, it did finally start again with the black smoke and all.
Made it home with no problems, but i am stumped.
Thinking of cleaning and rebuilding the carb to start.
Could there be too much fuel pump pressure??
Return fuel line not venting in the canister system?
Fuel mixture to lean/rich?
Have not messed with it for a few days, it does start right up but have not done anything.

 

[CruisinGA]

I doubt that was a rush of fumes, but rather a built up vaccum.

Try temp. running without the gas cap and see if that fixes it. (Could be a malfunctioning gas cap that is not venting, the built up vacuum in tank eventually is too strong for the fuel pump to overcome.

I don't think you're getting it hot enough to cause vapor lock, and the time it takes to start after opening gas cap would be because the pump has to re-fill the bowl.

Had same problem on my truck awhile back.

 

[offcamber40]

How fresh is your gas after your frame-off? Are you running a new fuel filter as well? When you did the restoration, did you replace or clean ou the gas tank, you may have some crud sloshing around that might cause an intermittent fuel problem. My Tank BTW always blows back out at me, not vacuum, and I have just lived with it, it doesnt cause me any problems. You may also want to fuel the fuel line going into the carb and pump it into a backet while having someone turn the engine over to see if you are getting adequate fuel flow. If all that has checked out ok, and you have re-timed it to spec, I would investigate the carb itself. I had an aftermarket one on mine that the float sludged to the bottom of the carb during my restoartion.. it took me forever to figure out why it was dumping fuel! I feel your pain man! Good luck.

Mike

 

[x-unimog404]

hmmmmmmmmmm, I did clean the tank out as best i could, I ran it several times, maybe two hours total before it tokk to the street. This is the first full tank of fuel on the road. I did put on a new fuel filter and all new fuel lines.Did not dissasemble the carb and clean.I did not replace the gas cap. Will have to get a new one and try that.

 

[fytattoo]

i was having an identicle problem with my 73...i purchased my 40 with a weber carb on it, the guy i got it from never hooked up the return line from the gas tank into aircleaner box...it had a bolt in it...at one point he had the tub painted and the paint guy lost a bunch of parts including the vapor canister that sits by the gas tank, they also had bolts in them...once i hooked up the return line it ran better but still built up pressure and i had fuel coming out the return and filling up the carb while it was sitting, and still had the swoosh of fuel vapor at the gas cap...once i vented the vapor canister lines it has been fine ever since...your vapor canister lines are those 3 lines right by the filler neck...alot of people remove them when removing alot of the polution stuff but they still need to vent...i put on oil breather filter off of one of the line and wire tied to the cage just above it for a quick fix until i find a way of better routing it....if check specter off road there is a half way decent diagram of the fuel system...maybe one of your lines didnt get hooked back up or is pinched off from the frame off

 

[x-unimog404]

All of the vapor canister lines were all cleaned, and put back together. There is a check valve that connects the line coming from the plastic canister with three lines, to the charcole canister mounted on the fender well. It was cleaned also, maybe it is not working and not allowing vapor to escape.. will check that.

 

[CruisinGA]

Don't bother with a new gas cap until you know that is the problem

Just run without one for a little while and see if that fixes it.