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Just got my quad back from the deal,had them install a dyno jet kit because I have fmf exhaust.they jetted the main to 128 from 120 and installed the dyno needle on the forth groove.I no this because they gave me the left over jets that come with the kit.i also read the direction that came with it.they put a k&n filter with a filter skin on it.they told me I could run with the air lid off.I took it out today and it bogged pretty bad on the low range,didnt work well at all.so I put the air lid back on and it ran well.I was wondering if its still jetted wrong or did I waste my money on these aftermarket breather parts.Or maybe I should do some adjustments.
 

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Personal opinion - you wasted your money unless you are racing and need extra top end.

Running with the air box lid off and the K&N filter are for top end performance enhancement. Modifications for top end come at the cost of low end. You can get rid of the bog by enrichening the air/fuel mixture on the low end. This is what happened when you put the air box lid back on. It increased the restriction to intake and slowed down the velocity of air passing through the carb allowing the passing air more time to pick up the fuel necessary to make the engine perform acceptably.

If you ride primarily on a MX track, increase the size of the pilot jet by one size and adjust the fuel screw for an acceptable idle. This might improve the low end.

If you ride in primarily dusty conditions, throw away the K&N filter (they pass more air, but they also pass more dirt and they need to be cleaned and re-oiled after every race), put the stock filter in and leave the top on the air box.

Just putting on the header will increase low end power, but the re-jetting is only necessary after riding it to see if it needs rejetting.

Another thing that will affect a bog on the low end is how the accelerator pump is adjusted or working. If the pump does not shoot gas down the throat of the carb immediately at the throttle is operated. a bog will occur.

Good luck
 
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