I have white brothers exhaust. K+N air filter. I have cut a 5 by 7 hole in the lid and covered the hole with fine mesh bronze screen. There is absolutey no restriction caused by the screening. Before I did the lid mod. The bike had a precharger on the air filter and an outerwear colver over the entire air box. I hadnt clened in for a several rides and I noticed that at 3/4 thottle on up that it was cutting out. Also, it was smoking black smoke. I assumed that I was running to rich due to lack of enough air. So, after cleaning the K+N and getting rid of the precharger, plus the mod to the lid cover I assume that there is plenty of air to draw from. Including the snorkle. I have noticed though, while running in while it is just sitting, if I pump the throttle fast, Im getting a bit of a pop out of the exhaust. Isnt this due to more unburnt fuel? I have 300 miles on this 400 since a top end rebuild. Could a new spark plug remedy this popping? I could shoot the designers that put that spark plug where they did. I dont have the spark plug wrench that came in the kit, and I am still trying to locate on. But, should I be blaming the plug or the jetting or what? I know that it has a .165 main jet but I dont know anything about the idle settings.