| dont know much about the banshee, is it still running the chinese plug ???. if so try a NGK or brand name plug & inspect how its running, it may be just jetting but a genuine dell would improve things im sure
but i could only suggest giving the fuel system a good flush out as they need to be done from new & a good quality plug to start with
the engine may be a little tight or it may be getting hot
try rebleeding the cooling system or flush it out as i have had a alloy radiator with casting sand or somthing in it from new.
also make sure the pump belt is in good nick & not streached perished or slipping,chinese oring belts can be a bit of a rough fit . | 
