lowbuck72

I am having a carb problem on one of my other cars which has me stumped. Maybe one of you experts can help me out. My problem is that it has dual carbs, but one carb starves for gas. The culprit is the fuel bowl inlet needle and seat valve. It seems to operate correctly in my hand when I blow through it and invert it. But when I put it back on the car, it runs fine for about a half a mile and then one carb starves for fuel again. I tried changing out the needle and seat valve but get the same result. The fuel bowl was empty, but had a lot of fuel pressure because gas went everywhere when I pulled the fuel line off. It has a mechanical fuel pump. which puts out about 5 psi. Could it be possible that there is too much fuel pressure acting on the needle and seat. Would installing a fuel pressure regulator help. The goofy thing is that the other carb works fine, and the motor has thousands of miles on it and has had no problems up to this point. I even tried installing a 3rd needle and seat valve and had the same problem.

74modified

First, I would have posted in tech/performance
Anyway, you should say what type carbs and a pic of the setup would be good.
Too much fuel pressure would overpower the needle and the carb would flood -opposite of what you say is happening.
Have you checked the adjustment of the float that shuts off the needle/seat? And you are sure fuel is getting to the carb?

Wrencher

yep, more specifics (type of carbs, etc), but very low float level will do that, or depending on setup, it may have a filter in the second carb that's restricting it. Just spit balling, very little to go on here.

MelWff

as others state more info but 5 psi is pretty low pressure.

REELAV8R

Agree. Check to see if the float has fuel in it. If it does it's sinking, cutting off fuel supply.

lowbuck72

Well, it's an air cooled VW with dual 40 mm solexes. Yes, when it starves for gas, the fuel bowl goes empty in that one carb. And, yes, one would think too much fuel pressure would flood the bowl instead, but it doesn't. That what makes no sense. I was thinking maybe excess pressure downward on the float might cause the float to bounce back with enough force to cause the needle to stick in the seat. I read where these carbs are happiest as 1 1/2 psi of fuel pressure, though I have never had any flooding problems. I was thinking maybe I should try swapping out needle and seats, or maybe floats between the two carbs and see if the problem moves from one carb to the other.