VCCA Home Forums TECHNICAL - GENERAL Mechanical - Engine, Trans, etc Float Needle Valve Seal Problems

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I am having difficulty getting a good seal between a steel tip float needle valve and a brass seat. It is on an aftermarket updraft carburetor (Tillotson).

Based on the information I can find (including CarbKing's website) the key issue is that the manufacturers have quit "coining" or "staking" the valve seat to give a uniform and smooth profile.

I have read multiple (and of course sometimes conflicting) ideas about how to fix the problem.
- Tap the valve to force the steel tip into the seat for a better fit. I did try this and it greatly improved the sealing. I was very cautious with how hard I "tapped" the valve.
- Use a Viton tipped needle (if you can find one that fits). There are mixed reviews on this solution.
- Put valve grinding compound on the steel tip and rotate the needle back and forth to lap the fit between the tip and the seat. Mixed reviews on this one also. You might damage the tip.
- Chuck a Q-tip with valve grinding compound in a drill and polish the seat.
- Use a steel ball (of the right diameter) and drive it into the seat.

I appreciate our thoughts and guidance on this. Right now the leakage is so slight that it does not affect the operation of the engine. The problem is that the float bowl will eventually overflow if you let the vehicle sit without turning off the fuel valve from the tank.

I think it's fine here Rusty. I'm afraid I can't help since I've not had to address that issue. Good luck.

Thanks Tiny!

This is definitely annoying me. I normally do very well with carb rebuilds.

Rusty,
If it was me I would tsp it harder . You said it made it better so it needs a little more.

Bruce

Rusty,
If it was me I would tap it harder . You said it made it better so it needs a little more.

Bruce

Rusty, I've been thinking about the issue. I like the lapping idea but I don't think lapping compound is what I'd use. I think it's too coarse. You might try it using jeweler's rouge.

Thanks for the encouragement. I have definitely improved the situation. This afternoon the carburetors did not show any signs of leakage after 15 minutes of leaving the fuel valve on without the engine running. It is a gravity fed system. Before my efforts today it would show leakage after 5 minutes.

I tired a few more things but I started with the old needle valve and seat. I figured that if I messed them up I still had the new ones to keep things going.

As Bruce suggested I decided to get a little more aggressive with the “staking” operation. One big difference was that this time I had the seat out of the carburetor and sitting on a piece of wood. The prior attempts to stake were with the seat in the top half of the carburetor. I was cautious because it did not want to damage the carburetor.

With the seat on the wood I could hit the needle pretty hard and not worry about damaging the face of the seat or the threads. I tapped the end of the needle valve pretty firmly using an aluminum punch. I did not want to damage the end of the needle valve that rides on the float arm.

My “check” was to pull a vacuum on the port where the fuel line attaches. The old needle leaked even worse than the new one. After my first attempt to stake it it improved quite a bit.

I next tried the Q-tip with very fine lapping compound on the seat. I ran that with the drill to polish the seat. Then I flushed it with carb cleaner. That took things wrong way. So I just rotated the needle in the seat with fine lapping compound. That improved hinges. After I cleaned that out I did one more “stake”, There is a definite mark visible on the tip of the needle. That held vacuum very well.

I attempted to get the new seat and needle to seal by heavier staking but did not have good results. So I put the carb together with the old needle and seat.