I have a '87 CH150. It has given me 85mpg in light riding, not goosing it all the time. My top speed is 10mph faster than 58mph. I've GPS'd my speedo @ 3mph low and pegged the needle at over 65mph today, so that was 68mph. I wish i'd had my GPS with me. It was pretty exciting. This engine responds well to opening it up for better breathing. I've removed the twisty intake tract and replaced it with a K&N filter on the carb. I've also opened up the exhaust a tiny bit. That's all I've done. Next, I'm opening up the muffler so that the outlet is as big as the head pipe. The outlet has less that half the area of the head pipe... the engine is choked. I also have a head I ported and polished and matched the intake manifold to the intake port, and head pipe to exhaust port.