Leaking fuel at carb

[Margie's68]

I rebuilt the carb on my 68 Cutlass over the winter because it would not idle. The car sat for many, many years and I thought there might by some dry rot in the gaskets, casuing a vaccum leak. The car idles good now, and the throttle response is much better; however, when the car is running it now leaks fuel from an opening in the top of the carb. I have tried the small hammer on the side of the carb trick, but it has not helped. It is an opening that is right above the plunger. I have attached a picture and put a green cirlce around the opening. Any thoughts on how to fix this, or why it might be happening? It is a 68 Cutlass-350CID-2bbl-A/T. Thank you in advance for any help that can be offered.

[Oldsguy]

Is that a picture before you rebuilt it? Hope so, because it is sure dirty and looks like you are missing a seal.

[Margie's68]

That is the carb before my rebuild, and during the disassembly. I had not taken any new pics, until now. I put the vavle back on when I rebuilt it it. The vavle is open when the engine is off, or at idle. The valve closes when the throttle is engaged. Is this the proper way for this to work? Maybe that is my problem, but I did take pictures prior to rebuilding it, and I reassembled it based on the picture. Thanks again

[Oldsguy]

I think that is correct function for that, as I recall it is a vent on the Rochester Dualjet. You may have a problem with a stuck needle which is allowing the fuel bowl to fill too much, it would make the fuel leak out the vent.

[Margie's68]

I removed the top and checked the needle and seat. It moves fine when I move the float up and down. I did readust the float settings, and reinstalled the top, but it still leaks. Is there an air/fule mixture screw that may be causing this problem? It surely seems like it is float/needle related but I have rechecked them. How about the jets; can they cause this problem? I did not replace those as they are not part of the kit. I am baffled, and with little carb experience I am stumped. Any help would be appreciated. Thanks again

[joe_padavano]

As Dan noted, that's a bowl vent from the bad old days before evaporative emissions equipment. The purpose is to let fuel vapors escape if the fuel in the float bowl started to boil due to heat soak from a hot engine, otherwise the increase in pressure would force the fuel into the engine and lead to flooding on a hot start. That's why the vent opens when the throttle is closed.

There's no adjustment for this, it's simply a hole in the top of the float bowl. If the float is set too high, you will get leakage, but it sounds like you've taken care of that. The problem may just be that today's gasoline is not designed for use in older cars like this. The gas is probably a little more volatile and as a result, generates vapors in the float bowl more readily. Any car built after 1970 has an evaporative cannister that collects these vapors, so you don't see the leakage. Is this leak a running dribble, or just wetness that accumulates on the carb? If the latter, there may not be anything you can do about it except be sure the float is set to the low end of the tolerance band. Also, did you replace the float when you rebuilt the carb? Additives in today's gasoline attack older floats and cause them to be heavier than spec, effectively making the float setting higher than spec.

[Margie's68]

Thanks for the tips folks. I talked to a well respected tech in my area who has been fixing cars for over 30 years, I know him well from my days at NAPA. He said it is definately a needle and seat/float problem and gave me a couple of things to try.

Joe, Thanks for the tip on what function that hole serves. I have been wondering what purpose a hole in the top of the float bowl would serve. As far as how much fuel fows out, let's put it this way; it's more like a stream of fuel-which also floods out the car unless I rev the engine. I did replace the float when I rebuilt it, I chose a brass one over the neophyl( or how ever you spell it) and although it moves the needle fine-it could be that the needle is not going up far enough to shut off the fuel.

I will try checking the float settings once again to see how they are. By the way, from the research I have done, the carb appears to be a number used on 1969 cars (7029156) and the kit came with 1969 float settings. Does anyone have, or no where I can get, the settings for a 68? Or are they the same settings? Thanks again

[Oldsguy]

I cannot imagine that the settings would be that different. Since you are addressing an excessive fuel problem though, if you have set the float at the '69 settings and it still floods perhaps you should drop it down about an eighth of an inch. Just an idea.....

[Margie's68]

The fuel leak is fixed. Although I had the float settings correct, the needle was not seating properly and fuel leaked passed it. I adjusted the arm on the float until I could not blow air by the seat, then I set the float properly. I am a nebie at this stuff, and I want to thank everyone for their help. Now I have a new problem that I will post in another section. Thanks