Seen a 200cc 4-stroke, 4 speed+reverse china engine on EBAY.
heres one
200cc and another
200cc and another
200cc and a
250cc one more
250cc so yeah there are engines out there if you friend wants to do one but I think the fuel tank is going to be close.
I'd like that engine except the 4 speed but reverse would be OK but then again reverse is not really needed on the lightweight blasters.
I can yank a blaster around pretty easily.(my sister might not be able to though)
I'm more excited about having electric start and a nice running 4-stroke in a nimble little blaster frame more than anything.
I'm just using the engine that I have handy but I just might be able to do another one since I had someone tell me tonight he has two non-running blasters he wants to sell.(cheap=$400)
This is really looking like an easy project compared to the one I did back in the 90's.
We have so many more parts out there than before.
I already have an exhaust that should be much easier to fit up.
K&N makes an air filter for just about anything now which was one of the problems I had back in the 90's blaster conversion.
The only real problem I see is engine / fuel tank clearance and the wiring but even wiring is no big deal.
I can get a 520 sprocket for the china engine so I can just run stock blaster #520 chain.