I've got several minis with small tires and things are geared way too low - more like a tractor or tiller than a minibike. I can't go smaller on the rear wheel sprocket. What is the largest stock #35 sprocket to fit a TAV2 without modification and where might it be purchased? Another thing, from sitting out under tarps my minis have a lot of corrosion on the engine blocks - what solution will clean that situation?