Originally Posted by Ghost0
I too had used the stock set up and never had a problem. Here are two tips above what had been mentioned. Your chain stay is typically not parallel to the chain. This would suggest that you need to twist the roller so it runs in line with the chain and not sideways. The other tip is to have the chain run on the bottom instead of the top side of the roller. That way if it slips it will slip to the outside of the bike and not into your spokes.
The only way you could achieve this is by reversing the bracket so it is on the inside of the chain between the chain & wheel with the roller on the outside but that would mean putting the bracket at an angle and inviting serious trouble. If the chain wants to jump off the tensioner then something is seriously wrong with your drive chain alignment, your chain itself, the sprockets or the tensioner or a combination of the above. On the HTs the drive sprockets are engineered by rice farmers and are notoriously uneven. It pays to work on them with a file to try and get the teeth evened up a bit before installing the motor. On all the kits the rear sprockets are not perfectly round and will always cause a bit of horizontal deviance in chain tension as they revolve. Sideways distortions can be corrected when mounting the rear sprocket by adjusting the bolt tensons but the up & down distortion can't really be corrected.