I have a zongshen 250, and again it blew up. It broke the rocker assembly.
I'm wondering there is a bigger atv engine that fits the cg 250 specs, like a 350-400cc??

 

I dont think there is, most of the 300cc and up engines seem to be based on Yamaha engines, except the BMS Tomahawk 400, which seems to be a direct knockoff of a Honda rancher, right down to bodywork and EPS! The latter's engine is a design that Honda started using in 1997, with the Foreman and 300EX models, and still uses in its latest Rancher. How BMS was able to use it in their quad without Honda bringing out the Lawyers is beyond me .

 

there is 300cc i think largest engine on china atv, but i heard it very fragile it self, and kind a too high fuel consumpion for that CC

 

A design patent lasts 14 years so a Chinese manufacturer can sell a clone beginning in 2012.

 

All they have to do is change one thing on the motor and now its no longer patent copying..

 

They used your idea todo alll stuff right now.