For those of you who read my previous thread I had a change of plans. I will mount a pushmower engine to my bike. I am now indecisive on the gear ratio again. I am using a compound gear system on a mountain bike so I could use the bike gears as a transmission by using a jackshaft that leads a chain to the gears. I'm thinking maybe 3.5 horsepower an 150 ccs. Maybe more. I will put a carb with adjustable throttle in place of the non adjustable one. I want to go as fast as possible, so I need a good gear ratio. And should I mess with the governor? Or leave as is? Plus when starting I start in the first gear? I keep hearing it oppositely. I want to go REALLY fast. Should I use a bigger motor? It will be a race bike/moped Haha

Hi,
Well, a jackshaft and reduction are in order. I built motocross bikes in the early '70s. The brakes are a definite concern. Disk brake bikes are extremely nice, and they stop better by an extreme degree. I will give you a link for reduction ratings; they are actually for belts. Small Briggs are better if you clean out the carbs and the ports; they have lots of inefficencies there from unclean castings. I did a 3 HP for a civic organization that tore up the competition. The carb was nonadjustable and had a scrow-ot pilot jet. Had to change it to a standard 5 HP model to get an idle and performance. See:
Pulley And Belt Information Calculator (http://www.csgnetwork.com/pulleybeltcalc.html)
Peace,
Clarke