External adjustment of the primary clutch spring on a Motorized Bicycle
I've attached some photos...my camera is really crappy but you'll be able to see how the thing works.
Basically the outer diameter of the main jackshaft has a fine thread. There is a collar that is threaded internally. Tightening or loosening the collar sets the preload for the primary clutch spring.
They used a high rate spring...which means that it is really stiff in short travel increments. Tighten the collar one turn and it makes a huge difference in the clutch pressure.
We had one engine that had a crazy stiff clutch. I've read posts where people have actually broken thier clutch handles. Our actuator knocked most of the stiffness away, but still I knew something wasn't right, as our other engines were fine, just like the first that we put together for a customer. We backed off of the collar 3 turns and the clutch was normal.
I have to emphasize that you do want back this collar off too far. It's impossible to totally unscrew it from the shaft, (while in the engine), but you don't want to put the assembly in a bind either.
The bottom line guys...Don't use this info to try and achieve a totally perfect clutch lever pull. The actuator is junk from the factory, and no amount of adjustment is going to totally negate the effect of the poor design of the original actuator. If you have broken a clutch lever, or you feel like it may break...give this a try! Even with the factory actuator your clutch should not be this tight!!!
Remove the clutch cable stanchion from the engine.
Remove the drive chain.
Have a helper hold in the clutch lever; or you can, of course, use the lock feature on the handle if it works well enough to fully disengage the clutch.
Through this hole, (where the cable stanchion mounts), you can insert a punch, 3/16" diameter or less, and catch one of the slots that has been milled into the threaded, (adjustable), collar. Hold the punch firmly.
Use a pair of channel locks to turn the sprocket in the same direction as if the engine were running. In other words countercockwse from this side of the engine.
Try one turn at a time...be certain to freewheel the shaft to ensure that nothing is binding.