I have a 150 gy6 on a carter gx 150 cart. It came in the shop with a no start problem. Took valve cover off found bearings had failed feel out. Put new stock cam in, now engine starts fine but will not take fuel . Called carter they said most likely cdi box so replaced cdi ,next maybe bad carb, replaced it too,still runs the same, good idle no power stumbles and wont take fuel, have set valves from .08-.12 have switched heads, have replaced crank shaft ,intake,flywheel,stator and pickup,coil,plug,two different cams all of these parts came off a good running cart, and parts were switched out and it runs fine.
Any suggestins would be much helpful.

Thanks Mike

have you checked the vacumn lines from the fuel tank to the carb. also the diaphram in the petcock may have a hole in it or there might be trash around the little filter in the fuel tank.

also if it has a stock intake check it real good for cracks

hope this helps

yes I have even switched tanks andvalve and hose ,I switched intae and carb as a assy, and the doner cart runs good.

Do a compression test?

110lbs

You set the valves to .003" for the intake and .004" for the exhaust? I'm stumped! Is the air filter wet or clogged?
I'd also check the timing again.

Ido not have air filter hooked up and i have removed muffler as well but did not help. advanceing cam 1 tooth lets you get 1/4 throttle responce. the engine has a different sound when running ,something like ehaust leak

2 bad e-chokes? When it idles, and you step on the gas, is it acting like the choke is still on and just dieing?

crankcase pressure is zero .vacume at idle is over 60 inches of water. do you know what voltage should be going to auto choke at start up and after warmed up this one has 6.84 at start up and slowly dropes as it warms up to around 4.5

Try this, take the choke off, the plate that holds it on and all, use a piece of gasket material and trim it to cover the all the holes on the choke plate. reinstall and see what happens.

If I remeber right if there is voltage at the choke after about 5-11 minutes it is defective. as long as there is voltage the wax in the top will never cool back down to release the pin back into closed postion.