I have a Tao Tao 125cc 4 stroke. Starts, idles fine. When I put it in gear press the brake the engine stalls. The brake sensor isn’t the problem. When its in neutral, the engine doesn’t stall. It only stalls if I press the brake while in any gear. It raised the back with a jack stand, placed it in gear then held the back tires. That also caused the engine to stall. I was thinking it could be the clutch. You can shift from 1,2,3 with no issue.