China Girl will not run unless choke on

You have a massive air (vacuum) leak somewhere. Either the carburetor to intake manifold or the manifold to cylinder gasket would be my first guesses.

If those areas have been sealed then start looking at your crankshaft seals. There are two; one behind the magneto rotor, the other behind the small, primary gear on the right side of the engine.
Anytime there is excess air entering downstream of the carburetor you will have the symptoms you describe.

What carburetor are you using and how did you seal it to the intake manifold?

Tom

Buzz,
Think of it this way: If the engine runs with the choke closed, lever up on the NT carb, then the engine is getting air from somewhere. There isn't sufficient air passing through that little hole in the choke plate to allow the engine to run. The engine dies when you open the choke because you're getting too much air to fuel, an extremely lean condition.

Now the challenge is to find out where that air is getting in. If the carburetor isn't sealed to the intake manifold by some method, sealant or an 'O' ring, it might well be there. If the intake manifold was installed with the kit supplied gasket that also is a common source of a leak. The kit gaskets are notorious for premature failure.

It appears that you have the chrome/steel intake manifold. They are almost without exception, warped from the welding process where the flange attaches to the tubular portion. That flange needs to be filed/ground/sanded flat to achieve a good gasket sealing surface. You might also want to closely inspect the intake manifold. Although I have only seen one, I found a bad weld on the flange and an opening that was a leak, albeit a small one.

Remove the left side magneto cover and inspect for evidence of oil residue. That would indicate a bad crankshaft seal. Not uncommon. On the right side, behind the small primary gear is another crank seal. Again, evidence of oil in this area would tell you the seal behind the gear is defective.

Tom

rogergendron1 said:

if you have the cns or any of its variants the choke is an enrichmant circut and adds fuel ! its backwards compared to other carbs

so if you have a cns carb and it runs with the choke on but not with it off then you are starving for fuel and are getting to mutch air, but with a nt or speed carb you are getting too mutch fuel and not enough air and turnning on the choke leans out the mix enough to let it run

Click to expand...

Because the OP has described his choke lever we'll have to conclude that he has an NT or NT Speed.

If you close the choke plate, lever up, you restrict the inlet air thereby causing a fuel rich condition. If the engine runs with the choke closed it must be getting air from another place other than through the carburetor inlet.

As said, relying on the clamp and a metal to metal connection between the NT carb and the intake manifold is asking for a vacuum leak. Even using an 'O' ring doesn't guarantee an air tight fit because the factory sometimes machines the slots in the carb outlet side too deep and leaves a space where the 'O' ring can't seal. I've seen this on two seperate carburetors. A gasoline compatible sealant is the best way to assure a good seal.
The problem with the 'O' ring method is getting and keeping the carburetor tight enough against it for it to do its job.

Tom