Hey everyone, im new to this website and just joined because ive been having some issues with my 07 Grizzly 660. So about a year ago I purchased my quad and since I got it ive installed a triangle atv snorkel kit, and a hmf performance slip on exhaust. So ive noticed since I installed the exhaust it slowly started to decrease in speed. It started at 55-60mph and then gradually went downhill. It backfires when it tops out so I didnt want to blow anything up when it got down to 32mph. Everyone has been telling me it is the jetting so I called hmf and they recommended a 175 small which is a big jump up from the stock 153.8. I put it in and tried to adjust the fuel/air mixture screw and it was way too much fuel. So this knocked it down to 12mph. At a 1/2 turn out it picked up the speed to 17mph. So this led me to put the stock 153.8 back in and adjusted the screw all the way out. This actually picked my speed up to 34mph, so I figured i need a slightly bigger jet. I put a 157.5 into it, and adjusting it a half turn out to 5 turns out and it stayed a steady 37mph and didnt change a bit. Im not sure my next move so if anyone can help me out it would be greatly appreciated. Thanks!