mini bike clutch/jackshaft help

[poppa]

Hi all. We have a mini bike with a 250cc Yamaha snowmobile engine. I am more interested in off the line performance than top end. It has a snowmobile clutch set up for the "primary drive" (with a belt) with a jackshaft for the "secondary" (with a chain). It has been in our storage unit for a few years and I hope to get it out this weekend. I want to finish it before I bring my car home. My question is , what size sprocket should I use on the jackshaft to reach my goal? The rear wheel is a 22" dia and about a foot wide . I do not know which size sprocket is on the rear wheel right now and I know this will make a difference. Maybe some examples for now??? Thanks