Carburetor leaking fuel!!!

[SBSerpent]

Originally Posted by TimG427

The needle and seat stuck on my Cobra right after our Austin get-together last weekend. Pulled it out and cleaned it off and it's fine now.

I gave mine a thorough cleaning as well and it moves smoothly but I still have a concern over the O-ring on the N&S assembly. I'm just gonna replace it entirely with a new one from the rebuild kit.

How did you realize your N&S were stuck? Was the car stumbling really bad? Smell of gas? Was it pouring through the boosters into the chambers?

[patrickt]

Originally Posted by SBSerpent

How did you realize your N&S were stuck? Was the car stumbling really bad? Smell of gas? Was it pouring through the boosters into the chambers?

Remember that any time fuel comes out of the boosters, when the butterflies are closed because you are idling, it will pool on top of the butterflies and then seep out through the throttle shaft and drip down on to the intake manifold. If you had a nickel for every post where some guy wrote "why is gas leaking out the side of my carb?" you'd be a millionaire. If it is on the secondary side on a vac secondary carb, it usually comes out the shaft and drips down off the plunger for the vacuum canister. If you look down the top of the carb while it is idling and you see little pools of gas on top of your butterflies then it means either your needle and seat is leaking or your floats are too high or the gas you are using is really $hitty and is percolating up and out through the boosters. A couple of years ago I did a full rebuild of my carb and set the floats dry on my bench. When I fired her up I set the floats to just at the base of the sight glass for both primary and secondary. Then I took her around the block three or four times and pulled her back in to the driveway (not the garage) and popped the hood and removed the air filter. Gas was dribbling out both primaries and secondaries at a pretty decent pace. I immediately shut her down and the prettiest white cloud formed about one foot over my carb that you have ever seen. If I had had a Lucky Strike in my hand I could have made a wonderful YouTube vid with it. In order for me to set my floats perfectly, so that I get no percolating after I shut her down on a hot day, I have to set the gas level about an eighth of an inch below the sight hole and the way I do it is by setting it just below the hole, then drive her, if she percs then set it a little lower, then repeat until both primary and secondary are set as high as possible without percolating out when hot.

[SBSerpent]

"then it means either your needle and seat is leaking or your floats are too high or the gas you are using is really $hitty and is percolating up and out through the boosters"

...or the O-ring on the N&S assembly may be leaking?

I experienced exactly what you described in your write-up but in my case, it was on a cold start (car hadn't been run in days), which takes the percolating gas factor out of the equation.

[patrickt]

Originally Posted by SBSerpent

"then it means either your needle and seat is leaking or your floats are too high or the gas you are using is really $hitty and is percolating up and out through the boosters"

...or the O-ring on the N&S assembly may be leaking?

I experienced exactly what you described in your write-up but in my case, it was on a cold start (car hadn't been run in days), which takes the percolating gas factor out of the equation.

Yep, that too.

[SBSerpent]

Carrying that thought a little further. When I placed the old N&S back into the fuel bowl, it just dropped right in up to the threaded portion with no resistance from the O-ring. Based on the recommendation of using a lubricant around the O-ring, I would think that the N&S assembly shouldn't just 'fall in' to the hole but rather needs to be pushed in due to the resistance from the O-ring. Shouldn't that be the case? If my old N&S just drops in, does that indicate a bad O-ring?

[SBSerpent]

Nevermind. I just realized that the O-ring doesn't start seating until you've tightened the N&S a few turns.

[Gaz64]

Originally Posted by SBSerpent

Carrying that thought a little further. When I placed the old N&S back into the fuel bowl, it just dropped right in up to the threaded portion with no resistance from the O-ring. Based on the recommendation of using a lubricant around the O-ring, I would think that the N&S assembly shouldn't just 'fall in' to the hole but rather needs to be pushed in due to the resistance from the O-ring. Shouldn't that be the case? If my old N&S just drops in, does that indicate a bad O-ring?

Yes, bad o-ring.
The o-ring needs to be the correct size, and lubed on assembly. It is the first resistive part on assembly.
A bad o-ring can be a reason for a creeping float level, and flooding condition.

[SBSerpent]

Originally Posted by Gaz64

Yes, bad o-ring.
The o-ring needs to be the correct size, and lubed on assembly. It is the first resistive part on assembly.
A bad o-ring can be a reason for a creeping float level, and flooding condition.

And a bad O-ring was the cause of my problem! When I compared the old N&S assembly to the new replacement part, the flatness of the O-ring was very obvious. I guess it had lost it's sealing capability over the years. Reinstalled the bowl with a new N&S and new gaskets and everything works great now. No fuel pouring into the secondary chambers. Thanks everyone for all of your help, proving once again what a wealth of information this forum is.