So, I'm a diesel mechanic and automotive technician; however, I don't have a lot of experience with these small engines. I'm working with a 2006 Brute Force 650 4x4i. At idle, warmed up, and choke off, there is a backfire type thing occurring. It sounds like a pop coming from the carburetor. I took the box off and I could see flames in the manifold, below the throttle plate (not your typical Edelbrock flame thrower). So, I took off the carb and looked at the boots; they were ripped and they were replaced. However, that did not solve the cough. So, I took the carb off again and pulled the plug to adjust the pilot screw. I made it super rich, but alas the pop remained (albeit at a much lower frequency). So, I think it must be lean still. So again the carb comes off to clean the pilot jet. There was a little dirt in the bowls, definitely not the worst I've seen, and I proceeded to clean the main and pilot jet as well as inspect the jet needle, diaphragm, and float plunger. Everything looked good and, while I had the carb off, decided to check valve lash--it was good. I then slapped the carb back on, and cuss words ensued--possibly some tools thrown. Anyways, my question is, before I completely rebuild the carb and clean the casting, is there anything else that could be causing this problem. I don't think you can adjust ignition timing on these quads, air filter and box are good, vacuum is good, fuel supply is good, and it's not in limp mode. The popping only occurs at idle (worse at low rpm, and better at high rpm), and when I hit the throttle, the quad ponies up and goes--sounds and performs perfect. Let me know what you think, and sorry for the long post.