I have a Ryker with the Ace 600 engine and have not had any issues. The 600 is an absolute hit, as far as I am concerned. The zero to 60 time is 5 seconds and I am getting 200 mi. on a tank of premium fuel. Because I don't see any complaints, on this thread, I would guess that others are enjoying trouble free miles and smiles on their 600 Rykers. I have clocked 6000 mi. on my first year of three wheeling. No more two wheels.