280cc...
the engine cant be bigger then 240cc , and if it would be bigger your jet would be way too small .
i have a 240 big bore kit and im runing a 370 main jet.
your engine is probably stock bored at .080 that means your jet is too big and thats why your engine bugs like that , if you check your sparkplug youll see that it is way too black , go get a 280 main jet and put it in your carb and check the plus , if its black you need a smaller het if its white you need a bigger jet , the sparkplug need to be a nice golden brown