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Discussion Starter · #1 ·
I need opinions on my tuning: I've got a 2000 400ex, original motor, wrapped header, oil change. Rebuilt the carb and adjusted valves. After a lot of trouble with backfiring through the carb (signifying really lean) I'm running a 42 pilot jet and a 150 main jet. This helped a lot, but I'm still about 3 turns out on the fuel/air screw and a hair on the idle adjustment. It still coughs tons through the carb when cold, and nearly runs right with choke on during a cold startup. But once significantly warmed up (like I need to throttle it for quite some time to get it hot enough) runs great, idles great, and the plug looks good. Lots of power, feels great. I haven't messed with adjusting the needle, but it is in the stock position. I have no leaks around the carb on either union. I'm kind of at a loss here, and tentative to up pilot jet anymore sizes since it is already pretty big. Opinions?
 

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Discussion Starter · #3 ·
Well that's the thing, my airbox lid is still on and I'm using an oiled uni foam air filter, stock muffler. I don't quite understand why I've needed to go so rich to obtain normal performance. It seems to me that you can obtain similar results by adjusting the needle like that of adjusting the fuel screw too.
 
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