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Discussion Starter #1
Ok guys been riding and working on polaris atvs for 19 years now and looking for some info on the jets. I just rebuilt my 2000 400 Xplorer 2 stroke and went .040 over and shaved the head .015. In addition it has the 400 scrambler exhaust from the head pipe to the silencer. The silencer is an FMF and im curious as to what jets u guys think i should use to get more power. Any opinions are appreciated.
 

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There are to many variables to get a good answer to that question. Start with something rich and work your way down.
 

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I'd start with what fmf recommends for jetting with their pipe. The bore isn't going to matter enough to worry. Shaving the head just means better gas, not more or less of it. You will probably end up 1-2 sizes larger on the main jet.
 

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Discussion Starter #4
Thanks guys. Ive been working on atvs for a long time just never done any jetting and didnt kno where to start. Thanks again for all the help! ??
 

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These links should get you started. The first one has an evaluation process that I found very straight forward. Try calculating your cylinder volume. Then take stock of the original jets and calculate an equal percentage if possible. The race guys would suggest that you only move up one matched set of jets at a time, but if you get numbers that support skipping the next jet size up it's something to consider. I included a purchase site link after seeing how much they have to offer and the price point looked pretty good too.

Jetting
Carburetor Jet Tuning Effectiveness Guide
Mikuni carburetor operation and tuning
Mikuni Jetting Info
Jets R Us mikuni, keihin, hitachi, holley, jets and carb parts
 
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