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Discussion Starter · #1 ·
Hello! New to this forum, just picked up my first 400 EX. 2003 model. I expect, like other machines, the stock jetting is a little lean. I'm putting a spark arrestor plate on the stock pipe (removes baffle) and leaving the rest stock. Should I bump the pilot for better cold starting? Maybe bump the main to 150? Also, if I put an outerwares airbox lid, how much further to take the jets? Thanks!
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Welcome to the forums. I wouldn't bother the pilot jet but definitely bump the main up to a 155 or 160 with the airbox and muffler mod. if you install an aftermarket exhaust then bump to a 170 main and 1/2 turn out on the air screw.
 

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Welcome to the forums.
 

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def listen to moose he was dead on with my jetting questions.... givin any thought to upgrading to a slip on pipe will boost your performance and still give you the spark arrestor... just posted a thread about the dmc afterburner i picked up and i got no complaints about it
 

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put in a 42 pilot jet. it will start easier and not be to rich.
 

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hey Moose, I need a secound opinion on my jetting. I have 12.5:1 416 piston, stage 2 hot cam, mild porting to head, stock size valves, sparks full exhaust 2" core, white bros cdi, k&n filter w/ outerwares and no lid. Before I started working crazy overtime I started to jet my carb but, I was using 114 octane leaded fuel which I quickly found burns gray not black so I never got the color I wanted on my plug. I am now to rich and need to run out some of the race gas and add 93 so I can get some color on my plug. What would you say whould be a good jet to start with?
 

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2000 trx 400ex / just rebuilt carb and noticed the jets are stock , 38 slow jet , 148 main jet . bought used and already has a white brothers slip on exhaust and a k&n air filter. looking at the info above i should change the main jet to a 170 ??
 

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Discussion Starter · #9 ·
Thanks for the input! I'm off to the jet store!
 
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