You might try googling "chainsaw engines on bicycles". I have in the past found tons of information on the subject there.
I haven't done this but here are some things I found out when researching it.
1.Chainsaw engines are high rpm some running well above 10,000 rpm so you'll probably need at least a two stage gear down.
2. Chainsaw clutches typically lock up from 1300 to 2300 rpm and they must lock up to stay cool. If they don't lock up they will destroy themselves pretty quick.
Try instructables.com also. Someone has done this I'm sure.
Good luck and have fun. Just building it will be fun and If it works even more fun.
