Re: SBP Shift Kit and Shimano Grip Shifters
If your shift kit has been recently installed, expect the chain to initially stretch a bit.
It will require some adjusting but yours sound like more than just a stretching chain.
When you look down the center-line of your bike is the engine( particularly the top of the cylinder head)
even on both sides of the top tube?
Is your bottom bracket tight?( Is there play in the pedal crank arm bearings?)
It sounds like something is loose and the motor is shifting.
Re-check all your mounting bolts.
I've had mine on for 6 or 7 hundred miles and finally got that chain to stay tight.
I'm sure Jim at SBP will help you if you give him a call.
I have a couple of times.
These guys are the best out there.
The best set up is with the rear derailler twist shifter on the left bar, with the clutch.
On the right bar get a dual pull brake lever for your brakes along with the throttle and kill switch.
The kit throttle and kill switch are plastic junk. When you break them get some decent ones from SBP.
Squeezing the brakes hard will eventually crack that plastic throttle housing.
That's my 2 cents worth..
Good luck and don't give up on it, the shift kit is the best thing you can do to make your bike FuN.