I really like the way this motor is turning out after 1 gallon it holds tune and runs 10 min on one tank also idles forever but I can't seem to smooth idle out all the way has a little pulse. Like I said I can deal with that I think it needs sealing around carb neck and pinch bolt. Anyway I am trying to figure out when is the right time to pull shim like it says in manual or just keep on running it? I don't understand why this motor didn't sell better it runs as good or better than any of the Werks standard B5/B6 motors and lasts longer for sure I got mine for $200 with coupon great deal! When are other owners removing the small shim from head on their R21? Thanks AGAIN!