Hi I like doing makeshift project so I decided to make a bike using a chainsaw motor. I need a little help though, I want to have some torque (I live in bloomington Indiana) to hit the hills but I also want speed to be able to ride on roads. I plan to mount the chainsaw on the rear rack of my 18 speed mountain bike. Now listen closely it gets complicated.
1. I will remove the pedal and weld new foot props.
2. I will instal a jackshaft with one large gear and a small gear behind that in place of the pedals (gears on right side).
3. I will wrap the chain from the chainsaw around the bigger gear.
4. I will wrap the chain to the original gear system around the small gear.
5. I now have a chainsaw bike with a transmission.

What I need to know:
1. what type of chainsaw to use (I want the bike to go up to 45-50 mph easily)
2. what size gears to use on the improvised drive shaft

I am not worried about the cc limitation on the chainsaw, just whatever will pull a 150 pound person without stalling or strain.

I will not buy a moped or motorcycle as I already have all the parts except for the chainsaw and gears.

Thanks very much!!

"40-50 MPH easily" and then stop with the bike brakes" Do you have a death wish? One little miscue and you are in trouble. Look at the history of Whizzer bikes to see how they worked.

I have that worked out I bought a set of advanced handbrakes and I know to knly stop with the back one gradually.

If you Google. "Whizzer bikes" you will see another listing for a complete motor and parts for $179. Also on YouTube.

I don't understand why you are not still using the back gears as they are, to allow you high and low gear ratio.

I am but I thought I would need a gear ratio for the 2 gears I would have on the jackshaft in place of the pedals that the chainsaw chain and chain to the gears would be connected.

I would go with the larger CC you can get, if you are getting too much, it can be handled by setting limits on the thottle, or handled though gear ratio

I think I will get a 70cc or a 60 and use a 20:1 gear ratio. What do you guys think?

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