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Discussion Starter · #1 ·
So I got a new 2008 trx400ex and I want to put a K&N air filter on it. when
I went to buy it the salesman said I should be Careful ,said that the new bikes are coming from Honda already on the lean side ,And if I put the new K&N on it, it could lean it out even more causing it be to lean So my ? is, could i just adjust the fuel mixture screw or do I need to re-jet just for the filter and if I can adjust the screw do I turn it in or out and how much?

Thanx ahead of time for any help:
 

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If it makes it too lean, then you will probably need to rejet. The fuel mixture screw just comes into play at idle. Above idle it does nothing.
 

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Discussion Starter · #3 ·
Thanx

Ive not done any rejetting would I just up size the main one size
 

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I would look at the spark plug first. If it's a light brown or tan, then I wouldn't go up on the jet size, but if it's not, you need to go up on the jet size until it is a light brown or tan. Open the bike up in high gear in a long stretch and then kill the engine with the kill switch, while still wide open. Then take the plug out and check the color. You only need to adjust the fuel mixture screw if you don't have a smooth idle.
 

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Go to Dynojet web site and look up the pdf on their site for the 400EX it will tell you what to jet it to if you bought one of their kits, if you do buy one of their kits the instructions come with it. if you change the filter you will have to go up on the main jet most definitely.
 

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Hey i need a hand on what jets to use. i have a 08 and just put a k and n on it and the air box pre filter on it that totally replaces the top of the air box. if i could get some info on wat jets to use that would be awesome.
 

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Hey i need a hand on what jets to use. i have a 08 and just put a k and n on it and the air box pre filter on it that totally replaces the top of the air box. if i could get some info on wat jets to use that would be awesome.
The answer has already been given in this post:

1997-2008 400EX Jet Kit

Be careful where you get your kits from, I just saw this on their site:

Dynojet Fraud Alert on Jet Kits

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