You could get a dax Gen IV engine for $129 and the rest of the kit parts off his site or just buy his F80 kit for $199 for the full kit...
Top left picture on his site... http://thatsdax.com/
, You really can't go wrong with his engines since he gets really nice ones with the bigger 40mm crank, upgraded bearings, upgraded hardware and all already installed.
I weigh around 220 and mine pushes me down the street really well.
If Dax is out of engines or kits, contact Motorbicycleracing in here, he sells high quality engines and kits as well, Both these sellers are top notch and their engines are the best China Girls you can get.