There is another Sticky thread posted at the top of the Gas Engines thread. There are several contributors
This thread should answer most of your questions about
GAS ENGINE OPERATION
Here is a "click on" link to the thread
http://www.rcuniverse.com/forum/m_8673009/tm.htm
There us another very good thread that answers a lot of questions and takes up the conversion of some popular engines some of which are chain saw engines
http://www.rcfaq.com/ANSWERS/ENGINES/WEEDIES.HTM