Your bike should have a #41 chain.
Some came with a #415 chain. Although it will work, it really is too big for the job.
A heavy duty
BMX chain will work as well. They are #41
The little clutch release pin in the center of the engine sprocket should stick out about 1cm or 7/16" or close to it.
If it does not, my best guess is you are missing the ball bearing that goes in the hole before it.
The bearing has to be in between the internal clutch release and the little rod sticking out of the center of the sprocket.
Check this out, you can see how it all works:
Thankyou Creative Engineering/ Manic Mechanic for making it!!!