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Discussion Starter · #1 ·
Hi everyone. I just put a new Modquad K&N air filter on my 400 ex. I bought it from Rocky Mountain Atv. I installed it properly and it fits tight and well. However when i hit the throttle hard it boggs down and almost stalls out. if i let it ride out slowly it will ride. And 1st and 2nd gear are better than 3-5. once i hit 3rd it wants to stall and i have to down shift. Do i need to jet it?
 

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Discussion Starter · #3 ·
oh it also was making a little cracking noise that i never heard from the engine after i shut it off. its brand new. i bought it in April. what is that? any clues?
 

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I would go up at least a couple sizes on thew main jet. The new filter is bring in more air, and it is being starved on fuel. Is that your only performance modification, I assume it is because I don't an aftermarket exhaust in your avatar. I'm not sure about 400ex jet sizes, but there are a bunch of people on here with modded 400exs that will be able to help you further.
 

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Discussion Starter · #5 ·
yes it is my first performance mod. Im not sure how to jet. Hopefully i can get some detailed advice
 

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Helmut usually has very detailed diagrams he finds. Other people will probably be able to help with the jetting on the honda carbs, they should be easier to tinker with than my Z400's (pain in the ass).
 

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Discussion Starter · #7 ·
Alright I just purchased HMF basic jetting kit. Does anyone know if this is a good one? I went with HMF because that is the pipe Im gonna go with as well later. Please give me info on jetting process. Is it hard.
 

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Jetting is pretty simple shut off the fuel first then locate the 17mm plug on the bottom of the carb unscrw that. you will leak fuel so put a rag under it on the crankcase. grab a 7mm socket and 1/4 drive ratchet if you take your finger and feel in the plug hole you will feel the main jet. now carefully remove the jet sometimes the jet holder will unscrew with it no worries it will go back. your stock jet should be a 148 I would bump up to a 152 or 155 turn the air screw out about 1/4 to 1/2 turn too it's right on the bottom of the carb towards the front of the engine beside the bowl in a recess. when you install the jet screw it in with the socket only then barely and I mean barely snug it or you WILL break the jet holder. now put the plug back in the bowl turn on the fuel give it about 30 sec to fill the bowl, start it and enjoy.You will need to take a plug reading to determine if you are rich or lean still. run the quad around easy letting it get up to operating temp, usually about 10 min or so. then find you a nice ling straight and open it up when you get to 5th wideopen hit the kill switch then pull in the clutch and stop, pull the plug and check the color, you are looking for a nice med brown (like Cardboard), if it's too dark pull the air box lid and put in a new plug and do the test again. if it's too light go up one jet size on the main and retest. Good luck Keep us updated.
 

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Discussion Starter · #9 ·
Ya I think I'm going to take it to someone. I don't want to mess it up.
 

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It's very easy to do. If u have any mechanical skills at all u can do this.Just try it every rider needs to learn to jet there quad.
 

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If you plan to put new exaust on, wait to jet. Put your stock air cleaner back on and order the pipe. Why re-jet twice?
 

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If you plan to put new exaust on, wait to jet. Put your stock air cleaner back on and order the pipe. Why re-jet twice?
What he said...especially if you're going to pay someone to do it. Whatever you decide, don't ride it with the K&N until after you rejet...you will damage your engine by running it lean.
 
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