This is regarding an 88 moto4 225c but that might something more general than this particular model. The problem that I have is if I go from neutral to first speed, the ATV start to go forward. Usually on these transmission, it will stay still until you give throttle, but now it's just keep going forward and can't stay still with no throttle opening. I've tried to put the wheel on jack, and was able to give throttle easily and shift through all gears 1-2-3-4-5 hi/lo fine. The only problem seem that it will always go forward no matter what. I've tried to unscrew 2 turn on the clutch pressure without any luck. Any clue?

 

Remove the clutch cover and check for rust and corrosion. Something is not allowing the clutch 'shoes' to retract completely from the drum. You don't say whether the machine is ridden regularly or if it sits alot. If ridden regularly, the clutch retrieval springs may need replacing, if it sits; the clutch needs to be dissasembled and cleaned.