with me on my jm... it was running lean and would always backfire and then i ajusted the aif flow screw and was running fine and i just re jeted and the back fireing went away but i havent relly ran it i have to replace bearings and shorten the chain and on top of that im grounded from it for 2 more weeks..... so im not shure how its running....... like it has alredy ben said.... i think u could have it done by a pro.