Sea Foam is good stuff, alot of people use it in outboards. I beleive that the reccommended usage of the sea foam is more than that of the Ring free, so check and see but they may work out to be about the same price. That is the ring free treats more gallons of gas per bottle than the sea foam.

Also I have read on other boards about the Yam OX sensors and they are pretty sensitive and expensive. Check around maybe someone can confirm that it is ok with the Yamaha engines but I think it should be.