50cc Runs then dies out

Chinese Moped 50cc 4 Stroke.

1. It starts up fine but if you leave it ticking over its dies out and stops.
2. If you keep the revs up it won't cut out but as soon as you let go it dies out and stops.
3. If you keep revs up and then come to a stop but keep revs up so it doesn't cut it won't accelerate again even if turning the throttle although it will tick over. But if you let the revs go it'll cut out.

I have cleaned the carburetor, changed the carburettor, changed the rollers, adjusted the air/fuel intake, adjusted the idle still no joy. Can't see any areas where air escaping engine.

Any ideas?

 

FIXED

After trying various things I finally fixed the moped and it runs perfect.

The problem was the exhaust valve setting. It was set at about .002 with the valve gauge so reset it at .004.

Started it up and away we go it worked great!