I'm working on an 02 Grizzly 660 and i have thoroughly cleaned the carb and put a rebuild kit in it along with a new diaphragm in top and on the side. My problem is the off idle/low speed performance. When trying to barely give it gas and ease around it stumbles and pops badly. My carb kit came with a 155 main instead of a 153.8 so i reused the old one. The muffler does have a large hole in it which may be some of my problem. Any advice would be appreciated.