i just want to bump this thread and add my .02.
i thought about this a bit, and rack mounting the motor is the way to go due to the pocketbike engines measurements. it is cramped to get one in a bmx frame, i thought about that a year ago. however, here is the rack mount kit i think would be best for PB engines, and i am a member on pbp i will attest to their reliability. they are really really easy to work on plain and simple, and if you know what your doing with them they will last a long time. i have 3 years on one stocker and it still starts up first pull and runs great! they just wont gernade like HTs will.
anyway, here is what i have found so far, i may not be eye pleasing but it works.
Golden Eagle Bike Engines, Geared Belt Drive Bicycle Engines / Motors for Mountain Bikes & More
i am still waiting to hear from them as far as if a pb engine will fit the setup, im sure it will. there are alot of GEBE fans on the "other site" ill ask them for a bolt to bolt measurement to compare with my pb engine.
ON THE OTHER HAND HOWEVER.....
im thinking, that it would be much easier to just buy a pocketbike as suggested, get it running, and cut it in half to make a pusher out of. you could then gear it for as much top end as possibble and probley get to 60kmh, which is exactly what im in the process of doing right now.
i will put a picture up tomorrow.
now for some good stuff,
a stock pb engine without ANY mods really is a well engineered little powerplant, They are peppy, and the centrifigual clutch will pick up speed rather fast if you back off the throttle and reaccel a few times.
remember, the centrifigual clutch slips, so to get up to speed, you have to release its grip and grab the drum again a few times before you have maximum speed.
a modified pocketbike engine with stiffer clutch springs engages harder. the best bang for your buck as far as just an engine can be found on ebay.
Mini Atv Quad Dirt Pocket Bike Big Bore Engine Parts !! on eBay.ca (item 290305868858 end time 24-Aug-09 01:02:33 EDT)
ADA clone motor, dellorto rep carb, 2 shoe clutch. thats your basic upgraded high comp pb engine.
oh, and my expert opinion like stated on pbp is that the pbu "race engines" are grossly overpriced. by about $300. so, you make the call there lol
!lastly, they STILL wont beat a morini, but they sound the same and perform just as good, just different! ill be watching this thread!