hi i have recently just acquired a Gemini SST 50cc. the motor runs fine but i am having problems when it come to the gears. the clutch works and also 1st and 4th gear work but it is not engaging 2nd and 3rd. occasionally it does go into them but not often. there is grinding when trying to find them. any help would be appreciated before i have to split the case which i probably will have to do.