Carb Drip

Sat Nov 16, 2013 2:26 pm

There is a steady drip from the "drip hole" at the bottom of the carburetor of my '50 Cub when I open the valve at the sediment bowl. Oh, and it won't start.

(Tank was off for interior cleaning and repaint, sediment bowl has new brass screen and gasket.)

Carb was cleaned and rebuilt with new gaskets, float pivot shaft and float needle valve w/ cage. Needle valve passed the try-to-blow-through-it test. Did NOT replace float, it seemed OK, although I did not try to test it. The drip started almost immediately, didn't seem like enough time for the float to take in gas and not float.

With sediment bowl valve closed, throttle wide open and choke open, it "burbles" when I run the starter, puffs of gray smoke out the exhaust, but it won't catch.

Does the drip mean the float bowl is overflowing, i.e. the float needle valve is not fully closing? Does that mean the float is bad? Or what?? Thanks in advance for your help!

Re: Carb Drip

Sat Nov 16, 2013 2:31 pm

P.S. The Cub hasn't run in a couple of years. Replaced points and condenser and spark looked good.
P.P.S. Pulled spark plug #4 and it was dry.

Re: Carb Drip

Sat Nov 16, 2013 3:50 pm

Your clues suggest a float problem. Dad did some work on his 49 Cub years ago. The kit included a new float and a template of some sort to use to set it. He didn't bother to use the template - thought a new float would be right. But he had to hook a pail below his carburetor to catch the gas. He was ticked at me for taking the carb apart and setting the float to the template - but it stopped leaking.

I had similar problems on my tractor last spring, but since it is my only lawn mowing machine I opted for a rebuilt carb. It was a little pricey but I certainly don't regret it.

Re: Carb Drip

Sat Nov 16, 2013 4:15 pm

Brian50 wrote:P.S. The Cub hasn't run in a couple of years.
First thing, compression test, dry then wet. Guessing valve or valves stuck, common problem.

Then check ignition timing. Static time or timing light.

Carburetor drip, could be in a couple of areas. Float level - fuel level to high, float binding on post or side of carburetor, leak at needle valve and seat or gasket under needle valve seat.

Re: Carb Drip

Sat Nov 16, 2013 5:51 pm

You don't mention anything about resetting the float height after replacing the needle and cage. Did you?

Does the needle and cage look like the one in this photo?


Re: Carb Drip

Sat Nov 16, 2013 7:41 pm

No, I did not check float height. Actually, I had the "drip" the last time it ran a couple of years ago, although I had never had that problem before, and I had never had any problems starting up prior to that. I can check the float height Monday - I'll be away tomorrow. Yes, the new needle assembly looks like your picture.

I can also do a compression test, but I think I confirmed all the valves were moving by looking in the spark plug holes while cranking. I will do that again to be sure.

The plugs are relatively new and they showed a decent spark - would it be worthwhile to replace them or is this a low enough compression engine to make that an unlikely problem?

Re: Carb Drip

Sat Nov 16, 2013 10:33 pm

Set the float according to this diagram.