gy6 50cc no power...
 

Hello, im repairing Jonway gy6 scooter for some guy.
First it was stuttering and i founded out that there was white plastic circle part that goes over the needle missing in the carburator.
I installed new one and scooter has stopped stuttering. But it still doesnt have any power. It goes around 20 - 30kph, it has realy bad acceleration and it goes on realy low rpm.
If I put scooter on the center stand, so wheel is up, it revs normaly, however if i press brake it instantly loses power.
I tried to play with air intake, but there is no difference. I checked valve cleareces and they are both OK. Also the camshaft is lined up as it should.
I can also hear some strange noise comming from under the flywheel I think.
What do you suggest me to do? Do you thing this could be CVT problem?
Thanks

Here we go again. Check vacuum lines. A engine that pulls well without load but dies when loaded is having a mixture problem. A cracked intake manifold or a vacuum line might be the problem. Spray WD-40 around the intake area and see if the idle changes or picks up.

Hello, thank you for anwser.
I thing that the manifold is good, because i changed it, but i will try with WD. I will also try to change vacuum lines. Thanks again

Hello, i checked vacuum lines and intake manifold and everything seems to be OK. After that i dyscovered that there was 84 jet installed instead of 79. So I installed 79. Now scooter wants to die when i turn the throttle. Choke is working, i also put in new spark plug and its the same. Old spark plug was black.
I also uploaded a video: https://youtu.be/JYDYN4kvKPk

Thanks.

UPDATE:
I founded out that the needle fall out of place, down on the jet. So i fixed that. It was a little bit better, but not much. Than i founded out that if i put electrical tape over inlet holls on airbox scooter goes almost good. Take off and mid-acceleration is good, but top end sucks. Something is wierd here haha. A replaced airbox, but nothing changed... Any suggestions? Thanks

check the compression and exhaust pipe gasket @ the head

I will and ill report later, thanks