Depends on the make, I guess. I expect a chainsaw will generally have higher compression, higher RPM range, and probably gobs of torque. The problem will be how to fit it to a bicycle. Its been done, a variety of ways, so I would guess that is where I'd start if I wanted to use such a motor.
Chainsaws generally have a small notched wheel running directly on the crankshaft, attached by a flatted, threaded shaft, with a locknut. You will have to use something else to either turn a standard bicycle chain, or mount some type of roller for use as a friction drive.
I have seen Youtube videos where users have welded a modified bicycle cassette sprocket to the clutch, and used the chainsaw, mounted on a cheap bicycle rack, to turn either a Happytime sprocket, or the front crankset. Dangerous territory there!
This video shows a chainsaw motor driving the tire with the actual clutch!
http://www.youtube.com/watch?v=cqu3vG-DrfY&feature=related
If you can order a Bike Motor Parts rack drive, you can use dozens of standard auger, 2 cycle air pump/water pump engines, pocketbike engines, etc, but I haven't heard of a chainsaw engine that has the same mount holes and clutch.
www.bikemotorparts.com
http://www.youtube.com/watch?v=zeofT8lUmAY
Home made friction drive from junkyard chainsaw. Looks like the standard BMX axle peg for a roller. This would work well, but eventually wear the bearings, and if the nut on the peg loosens, the axle peg can be thrown violently. "Check your nuts!"
