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Old 10-17-2012, 03:33 PM   #1 (permalink)
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400ex exhaust and jets

Hey i have a 2004 honda 400ex and i am getting a fmf power core 4 slip on for it. Do i need to rejet my carb and if so what size jets would be best. Thanks
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Old 10-17-2012, 06:15 PM   #2 (permalink)
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Yes you need to rejet your carb around a 165-170 should be a good place to start but you could go larger depending on other things that you have on your bike.
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Old 10-17-2012, 06:18 PM   #3 (permalink)
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the four wheeler is completely stock and to my understanding there are 2 or 3 jets not just one. Do the other need to be adjusted or replaced with bigger ones. Thanks for the reply.
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Old 10-17-2012, 06:26 PM   #4 (permalink)
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Well most people put a larger pilot jet in to make the 400 not so cold blooded.You can upgrade to a 42 pilot as far as a needle adjustment you won't have to adjust it at all.
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Old 10-17-2012, 06:32 PM   #5 (permalink)
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so if i put a 42 pilot jet in and a 165 in it what will the performance boost be. i will also have the fmf slip on
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Old 10-17-2012, 06:36 PM   #6 (permalink)
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I'm not sure I've never road a stock 400ex.You may need a larger main jet it just depends on how your plug reads but a 165 would be a starting place.
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Old 10-17-2012, 06:38 PM   #7 (permalink)
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alright thanks that is a huge help so would you say to put in the 165 with the slip on and ride it for a bit then check the plug and adjust from there? what adjustment should be made if its too rich or too lean?
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Old 10-17-2012, 06:41 PM   #8 (permalink)
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If it's too rich then you need a smaller main and if it's too lean you need a larger main.This time of year you will probably want to be on the rich side because of the weather getting colder.Then in the summer you can pull your air box lid and probably be dialed in for the hot summer weather.
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Old 10-17-2012, 06:44 PM   #9 (permalink)
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alright and the main jet is the 40 or 42 ?
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Old 10-17-2012, 06:49 PM   #10 (permalink)
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No that is the pilot jet which is for idle.Altitude makes a difference also so if you are at higher elevations then you will have to adjust for that too.
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