Re: please help.. locking screw is stuck..
You realize this is a 2 STROKE right? This means you need to mix oil and gas together, otherwise you don't have any lubrication. No wonder your engine isn't running right. You ruined it putting straight gas in there... I'm amazed you were able to make it 5 tanks. But you need a new engine. This time, mix the oil...something like 24:1 for break in and 32:1 or 40:1 afterwards.
They call these Power Assisted Bikes....Wait, who's assisting who? Last time I checked, I spend twice as much time in the garage working on it than I do riding it! Vista Out.