Why does my needle valve stick...?

[Bob N]

...or do I have some other problem?

Don, I have had a problem on several occasions--the latest yesterday--with what appears to be a sticking needle valve in the carburetor. It seems to happen when I throttle back and run slowly. A couple of weeks ago it stranded me on the water and I had to get towed in (I was not going to "troubleshoot" the carb when the engine was hot!). Each time, after stalling, the engine will not restart. It has good spark and compression. When I open the main passage plug, the carburetor is bone dry. The electric fuel pump is working normally. I have seen in the forum that others have had the problem and that they suspect that ethanol is softening the rubber/plastic tip on the needle. I suspect the same thing. The frustrating thing for me is that by the time I get the carb apart, the needle has freed itself so I can't absolutely confirm what is going on--yet the old-fashioned remedy of tapping on the side of the carb doesn't seem to unstick it.

Could there be some other problem? Can the float itself hang up and not drop as the fuel is used? Why does it happen only at slow speeds? (My theory is that at normally cruising speed the pressure of the gas entering the carb is strong enough to overcome the tendency of the needle to stick in the seat.) I have a 10 micron Racor filter and one of your "polishing" filters. The gas that comes from the fuel pump looks to be grit-free.

Do you have needles available that do not have the rubber/plastic tip?

[Don Moyer]

Bob,

I do have in my possession a solid steel needle I could send you for a test,
but I'm reluctant to start down that road at this time. Zenith dropped the
steel needles for what appear to have been good reasons when they moved
from the early model carburetors in the late 1960's. The solid steel needles
were apparently prone to allow some seepage. They have been providing
rubber-tipped needles in their needle and seat kits for early model
carburetors in recent years as well.

I've been trying to reach Zenith tech service to get an update on any
experience they may have had with Ethanol fuel. As of a year or so ago
when I discussed the Ethanol factor with them, they were not reporting any
problems with the rubber-tipped needles or with their gaskets.

Don

[Bob N]

Thanks, Don. I trust your judgment. If there is the possibility of the non-rubber tipped needle seeping, it sounds like that might be risky. Besides, it would be impossible to know whether the different needle really fixed the problem. If it happens again, I will try taking the carb apart and examining the needle closely. Perhaps polishing the seat again might help? I did that last year, but not this summer. I'll be interested to hear what Zenith has to say.

--Bob N