I get questions about fuel leaking at the throttle shaft often. This time it is a question about the Carter W-1 carburetor leaking fuel past the throttle shaft.
The cause is simple. There is too much fuel entering the carburetor throat. We call it flooding. The fuel is dripping on the throttle plate and running down the shaft. No, the throttle shaft should not be so tight that fuel can’t get past it. The shaft must be free enough to allow it to return easily when letting up on the gas. There is always some sort of gap between the shaft and the throttle body.
Flooding is caused by too much fuel entering the carburetor and flooding over and there is a short list of things that will cause this, but with the W-1, the most likely cause is a dirty carburetor. Carburetors are the ultimate fuel filter and the W-1 is especially good at it and I suspect it is because there usually isn’t any fuel filter between the gas tank and the carburetor.
I once had a W-1 that I had rebuilt returned to me because it ran great for a few miles, then started to run very rough, coughing and sputtering. When I took the top off I was amazed at how much crud was in the float bowl. There was literally no room for any gasoline. It seems the mechanic replaced the fuel sending unit at the gas tank, which loosened up a lot of rust and it all ended up in the carburetor.
Cleaning and replacing the parts included in our carburetor kit will most likely take care of a flooding problem caused by dirt.
Other possible causes might be a bad float. Be sure to test it by placing it in hot (pre boiling) water and look for any bubbles. Another possibility that would be low on the list would be a fuel pump putting out too much pressure. This might be especially suspect if you recently replaced the pump. Find the specifications for your vehicle and test the pressure and the volume.
Back to the throttle shaft. Test it by spraying some carburetor cleaner around the shaft and see if the RPM fluctuates at idle. Being able to wiggle the shaft back and forth more than say 1/32″ could be an indication the shaft is worn.
So, bottom line is that you have to think about the cause of a leaky shaft and not be too quick to blame the shaft itself. Actually, I have found the W-1 stands up well as compared to other types of carburetors.