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Discussion Starter · #1 ·
Just bought a 2003 400ex with a full fmf titanium exhaust. planning on getting a filter kit for it. what should the jets be? and anything else i should do to it and what other mods are good bang for ur buck?
 

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The pilot and mid range jetting should be fine stock. Might want to go up 2 sizes from stock on the main jet. Once you have installed a new intake system you might have to go up 1 size from stock on the pilot jet, maybe raise the slide needle 1 notch for mid range and maybe go up another 2 sizes on the main jet. Biggest "bang for the buck" is the exhaust and intake. If you need more top end, get a cam and if you want more bottom end, bore it. Good luck.
 

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Discussion Starter · #4 ·
Thanks for the help guys. next week on my days off im gonna clean carbs put new jets in get some better gas in it and go for a rip.
 

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Just use Hi-test pump gas. 93 octane is sufficient. You will lose power and the engine will run hot if you use over 99 octane. Try to stay away from alchohol blended gas if possible. (I could write a book on the problems alcohol can cause.) Also always shut your gas off when parking and drain your carb when the machine is not going to be ridden for a few days. A dry carb will not gum up. Happy trails :)
 
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