Discussion Starter · #1 ·
I have a 2004 400ex. It has a White Brothers Full Exhaust. I have a uni foam air filter on it with the air box lid on. Carb has a 155 main and 42 pilot jet. Everything else is stock however I have the air/fuel mixture at 3 turns as it runs better there than any other position I tried. Everything in the motor is stock and valves are in spec. I am having problems with getting it running correctly. It starts right up with or without choke, however without choke it backfires and pops and cuts out with throttle but will stay running at idle. With the choke turned on it runs good with only a slight pop in the exhaust when you really give it throttle. Sometimes the idle will suddenly slow down for 5 seconds and then go back to normal. Some other things I’ve noticed is there is a sort of whistling noise happening somewhere that sounds like it’s around the top of the engine. And finally I’ve noticed that the quads idle goes way up with the choke off and lowers when the choke is on which is the opposite of any of my past experiences on other quads. I am really looking for any thoughts on what is happening. Obviously it seems like it is starving for gas but it seems like my jets are plenty big and I’ve seen lots of other people running the same set up.