I suspect that you are referring to a common 66/80cc in frame engine. If so, the answer would be strong-NO. Don't even try it. Now, that being said... If you are talented with a welder, ingenious, patient and very creative, it might be possible. Because of the rear suspension, you absolutely can not fit the engine in that frame. If it is at all possible for the engine to be mounted on that bike, you would have to do something quite funky to mount it on a rack type system over the rear tire.
Its just not worth it. If you are set on the bike, look at a 4cycle rack mounted system but it will cost you more. Suggestion would be to try to find a garage sale/craigslist mountain bike with the old v frame and 1-1.25" tubes.