uuuuggh!! starts but wont run!!

Depends on a few things. Check your choke lever, make sure you've got it set right. You may wanna check the plug and see if it's wet, which would mean it's probably getting too rich of a mixture.

try unscrewing your gas cap and if it stays running, thats the problem. These gas caps dont vent correctly.

I agree with gas cap idea. I had that problem.

Take the bowl off your carb and make shure jet is screwed in properly.

And make sure your fuel filter isn't strangling the flow too much.

All above could be a possibility...and a vacuum leak, especially around the carburetor to manifold.

When the engine is to rich it will start very easy but bog when throttled. Usually jet problem.
When the engine is lean it tends to be very hard to start. When started it usually will race. If you can get it running . Apply half choke and see if it runs better. If so you have an air leak some wear.

Hey got the same problem,but mine won't stay running to adjust the idle screw.I have just got this nt from ebay seller .I think it's a air leak.I'm not sure tho.I looked in the were the intake mounts and there's no spacer of rubber washer but is it supose to on a nt carb......thanks

Adjusting the New 2011 CNS V2 Carburetor , It sounds like the choke! When its cold turn the choke lever on then when you get it started turn it off but not all the way off. Or till it warms up to what seams the operating temperature. As it warms up turn it off, or almost all the way off. The choke when all the way On is cable pulled. Off is cable not pulled. If the mini handlebar choke lever does not hold tighten the screw on the choke lever. Also you might have to find the right position of the C clip on the needle valve on the slide pin. Then adjust the air fuel mixture screw and the idle screw. The C clip has 4-5 positions, richer means more fuel has more power off the line, leaner means less fuel winds up more RPMs on the top end, find the best position. Move the C clip down is richer, clip up is leaner. In other words if the needle w/ the C clip on the slide is longer on the bottom of the slide it is leaner as it goes deeper in the jet hole. Leaner thinner is less fuel. Also the engine needs to go through the break-in period about 2-4 Tanks or 1-2 gallons then it starts to run better. Also make sure your clutch is adjusted correctly. In other words if there is a little drag at an idle it will stall the engine. How to test! At an Idle hold up the rear wheel of the bike if the wheel turns w/ the clutch in pin lock position then there is a drag on the engine. Try adjusting the clutch cable or the clutch. There should be no drag on the engine at an idle. Then adjust the air fuel mixture screw and idle screw.
Hope this helps someone!

Here's what I think you should try first:

Is this the first time you've ran a bicycle engine? It could be that you think it's firing up when you're really just hearing the piston go up and down. Try disconnecting the kill switch because it might be faulty and preventing a spark.

If that doesn't work, open up the bottom of your carb and make sure the jet is screwed in properly. Make sure it's screwed in tight.

If it's not either of those things, check for an air leak either around the carb or the head gasket. Also, are you using the stock spark plug? It could be a bad plug, so you could always spend a few bucks at NAPA and try running a good NGK plug.