Jim, I just mounted my new 3W 100 and had the same problem. I finnally used 1/4 x 20 allen head bolts. I wouldn't trust a 10 size bolt on this size engine. Wait until you try to run a throttle line to the carb. I had problems with the throttle locking up at full throttle(not running) due to the pivot of the throttle arm being straight back in the full open position. Had to raise the throttle nyrod higher so it could push down on the carb. arm. This of course was with the throttle spring disconnected. Connected had no problem but was causing the servo to chatter as if in a bind.
Carroll

Starting to wish I had bought the DA 100 Instead.......