Everyone has given good advice.

I would suggest as has already been done, stick with a commerical product first and then experiment.

I would suggest you start with a PAW .061 ( 1CC) from Eric Clutton (Dr. Diesel) http://www.cafes.net/doctordiesel/
or Ed Carlson http://www.carlsonengineimports.net/

Might seem a bit pricey to start but they are good investments, well built, reliable, and easy handling. Make sure you get one with the exhuast collect ring as that will help reduce the exhuast residue somewhat ( the 049 and 061 don't have mufflers but rather just a collecter ring.

Once you get comfortable with and are an old hand at running your small PAW you can then start experimenting with conversions.

Good luck, these engines are addictive.

cheers, Graham in Embrun near Ottawa Canada