Carb or Governor

Mon Jul 19, 2004 10:02 am

My cub would idle fine but you had to run the choke about half closed to get the engine to rev up. I rebuilt the carb with the IH kit and had the same problem.

I decided the compression was to low and sent the engine to the machine shop to be bored and the crank turned. I put all new pistons, bearings -- a complete rebuild.

I took the Governor apart to clean and inspect it. There was a pin in the governer that had came out and I put it back in during cleaning and reassembly

The Cub cranks and idles like a dream, but it still will not take the throttle unless you run the choke about half closed.

Do I have a gas/carb problem or do I have a governor/timing problem?

Bobby W.
Shreveport La

Mon Jul 19, 2004 10:22 am

I'd bet on a carb or fuel supply problem. Either a plugged main jet, float too low, inadequate supply of gas or even an air infiltration due to poor gasket surface seal at the carb / manifold. At least it's a place to start.

Mon Jul 19, 2004 12:45 pm

A #66 drill works great to clean the main jet, use it in a pin vise and turn gently by hand. It fixed my surging problem.

Mon Jul 19, 2004 1:43 pm

Try disconnecting the governor rod and see if it will rev up by just opening the throttle by hand. If it won't, then the carb or a large air leak is the problem.


Mon Jul 19, 2004 3:39 pm

Thank you everyone for the replies to my message. I will put my efforts toward the carb and try the suggestions you gave me.

I will post my results.

thanks again


Tue Jul 20, 2004 8:49 am

The Carb would not rev the engine without the governor hooked to it, so the problem is with the carb. I pulled the carb apart and cleaned the main jet and other pieces.

The engine will rev now, without the choke, to about half-way . A real improvement!! When you go beyond that it starts to lug down and you have to choke it.

I am using a small auxillary tank and have good gas flow, The fuel level (using Lurker Carl's method) is right on the money.

Any other suggestions?


Tue Jul 20, 2004 9:02 am

I had a similar problem. I couldn't get it to rev up when I opened the carb. I made a slight adjustment to the idle adjustment screw. I turned it out about half a turn. It works fine now, maybe a little rich at idle though. But runs great under load.

Tue Jul 20, 2004 9:21 am

I'd start looking for an air infiltration source. If the fuel level in the bowl stays up, your fuel supply is good. Either the fuel isn't getting through the main jet or there is too much air in the mix from a leaking manifold or gasket.