TheSamba.com :: View topic - possible fuel venting problem help please!Caution long post

Thu Mar 18, 2010 8:54 pm

Hi All, I just finished a complete rebuild to the motor on a 1974 1600 dp, in a SB. After the initial start up, and fine tuning, I took it for a short ride, just around the block, less than a half mile. I was running very good. I pulled back into the garage and it began to stumble and eventually stalled. I tried to restart and after a few minutes it started and blew out a dark cloud, it ran a few more seconds and stalled. I pulled the air cleaner and noticed fuel coming out the bowl vent. Then fuel started coming out of the carb like the float was way too high. I heard loud gurgling sounds while this was going on. The motor was not very hot at all. I took small vice grips and tried to pinch the fuel feed to see if the fuel would stop, then I took the fuel cap off and heard a loud burp from the motor although the cap made no noise when I removed it. This Immediately stopped the fuel leaking out the carb. I put it away to let it cool, and think of my attack plan. It appears the small ride jostled the fuel, created pressure and started this. Is there any venting I should be looking for? The cap is a non vented screw in type. During the rebuild, I bought a new brocar(sp?) carb, which replaced the mexican brocar that was already on it. I don't think it is the carb, as it ran very good for a while as I timed it, played with settings, rechecked time and so on. Any input would be appreciated. Thanks, Rich

Fri Mar 19, 2010 6:15 am

Hmmmm.. it's difficult to believe that the venting system could cause this big of a problem, but guess anything is possible.
Do a search on here. There's a fairly "elaborate" tank venting system in a '74 super...lines that go up to the expansion chamber on the cowl (in front of windshield wiper motor/fresh air fan) and a flexible line that should go to the charcoal cannister under the passenger rear fender. That cannister is then connected to both the air filter and the fan shroud using two large flex lines.

Trace your venting system from tank (3 separate vent lines) all the way through to make sure a PO didn't do something strange. :P

I'd still think that if it was truly a tank venting problem, you'd "hear" it when you slowly unscrew the gas cap.

Fri Mar 19, 2010 6:24 am

whats your fuel pressure like? Also, possible junk in needle valve preventing it from closing - If you have a junk gas cap, you could drill a small hole in it to act as the vent to elimiate your venting system as well.

Fri Mar 19, 2010 10:24 pm

Thanks for the replies. I like to finish my posts as maybe someone can gain something from it. This was a crazy one. I have an original evap system. The line that goes to the air filter was plugged solid. I did not have it connected or I may have noticed. I did however have the one hose connected to the fan shroud. Being the one end was plugged, and air was blowing in the other end, it was actually pressurizing the tank. Not a lot, but enough to create positive pressure. I tried it again and same result. Then I simply took the small vent hose off and blew thru it to see if it was clear and left it off. No more pressure in tank, no more flooding or problem. Car runs great again. I would imagine there is something wrong with the canister so I will replace it. There is a great article here on how to "recharge" the canister. I want to start with one without a known problem though. Thanks for your input.

Fri Mar 19, 2010 10:36 pm

redlightrich wrote: Thanks for the replies. I like to finish my posts as maybe someone can gain something from it. This was a crazy one. I have an original evap system. The line that goes to the air filter was plugged solid. I did not have it connected or I may have noticed. I did however have the one hose connected to the fan shroud. Being the one end was plugged, and air was blowing in the other end, it was actually pressurizing the tank. Not a lot, but enough to create positive pressure. I tried it again and same result. Then I simply took the small vent hose off and blew thru it to see if it was clear and left it off. No more pressure in tank, no more flooding or problem. Car runs great again. I would imagine there is something wrong with the canister so I will replace it. There is a great article here on how to "recharge" the canister. I want to start with one without a known problem though. Thanks for your input.

Yay! I win! I guessed a plugged vent line before i scrolled down :D

You could just get a charcoal can from another car, you know. They're just a container holding some carbon fragments. You only need a few fittings you can screw into the top.