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YZ426man

jetting

2 posts in this topic

FMF should have jetting recommendations on their web site to guide you. Just guessing, I would imagine that you would not have to change either pilot or main jet more than one size. Keep an open mind that changing jets alone may not attain optimum performance using the FMF pipe. Another factor to consider is the needle clip postion. If you look at your manual's carb tuning section, it shows little graphs that illustrate how each circuit works and how making changes affect the engine's performance vs RPM and load. As you try different settings and test the bike, it should become clearer to you what those graphs mean. Make one change at a time and then test, . . or you will end up chasing your tail.

When it comes to jetting, the best method is to try and get into the rich setting per jet and feel what the engine runs like when too rich. It will blubber and be kinda soft. Then, work your way gradually down one step leaner until the engine carbuerates cleanly. Keep in mind that changing the pilot jet affect the entire range because fuel is ALWAYS flowing through the pilot circuit. You can see this in the tuning graph. Good luck and don't be afraid to experiment. Keep written records as you go and you should be fine.

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