Re: Long trip planned-- advice welcome!
My perspective on this is that I wouldn't much enjoy trying to do a major fix on the side of the road. Do your already have a bike you want to use? That might suggest what kind of engine to go with. If you don't have enough money to set up a safe and pretty reliable ride (solid frame, good wheels and tires, good brakes and I would also want good lights). I've used both HT and four strokes (greyhound and HS) and my vote would be for the four stroke and an EZ transmission. How handy are you? You can buy the transmission by itself and use a greyhound engine if you're fairly handy. Depending on whether or not you also have to buy the bike, wheels, etc. you can get by pretty low budget. I have around $500.00 in a Greyhound & Qmatic transmission, low budget 12 G. wheels on a 51 Schwinn cantilever. The bike was free and I scrounged stuff, like rebuilding an old seat, using a rear drive sprocket off of an exercise bike... that sort of thing. I don't think that spending the least possible makes good sense on a long road trip like this, although you can be frugal and get a lot of bang for your buck. Canada has banned gas motored bicycles, so you may want to turn around when you hit the border. Electric is OK (within the law), but way expensive. Have a safe and grand adventure!
Someday when I grow up I will probably lose interest in toys with wheels, but until then...