Low end troubles
 

So I'm having some troubles on the low end. 150 cc chinese bike. Starts fine, idles horribly. Struggles to idle and has spurts of high idle here and there. When I open the throttle the scooter stalls and shuts off. However, when I leave it on for a while and warm it up, the idle starts to pick up and then it idles beautifully, almost too strongly. The problem at the low end still remains though. It has a delay - open up the throttle slightly and nothing happens for half a second, then the rpms pick up. Getting past the low RPMs on wider open throttles everything is perfect.

Do you have an auto-enricher (auto-choke) on the carb? I've seen this problem several times with these devices. I know some folks have a way of disabling them but they're cheap to buy and easy to replace so I've just taken to replacing them every once and a while.

I would check the intake manifold. I had one crack on me and it caused hard starting, surging and the idle speed to drop off. The valves should be checked first, as he said.