Beats me. I know that 20 years ago snowmobile manufacturers went to 4 stroke engines to comply with emission regulations, and also etec type 2 strokes. It baffles me that manufacturers can't make an engine that accomodates ethanol . Hope this doesn't bite me in the ass but I have a 60 4 stroke outboard 12 years old and a 135 hp snowmobile the same. Always ran the cheapest gas I could get and never an additive. Shut them off at end of season with whatever gas was left in the tank and started again next season and rode away. Did annual maintenance and took care of stuff but thats it. 30,000 km on the snowmobile and runs like new, no idea on hours on the outboard but a few