There is a book(let) put out by the IMAA called the "IMAA Giant Scale Handbook" that has a chapter on converting a Poulan Weed Eater engine to flight-ready. They install it in an Einducker - kind of a giant scale box-fuselage S.P.A.D. A little more involved than just stripping off the plastic and they walk you through it well.

The handbook has other good tips but, unfortunately, has a large section devoted to "currently available" servos and engines - many of which are no longer available and therefore wasted space in the book. Good info on coverings, compatable paints and setting up a pull-pull arrancement (Ackerman Effect explained well).