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Discussion Starter · #1 ·
Hi, new here. I have a 05 400 ex w/ a few small mods and having a problem when WOT.:confused: It runs great all other times.

If im toped out in fifth and WOT for a little while, it will begin to cut out like its running out of gas. If I pull the clutch and give it a few revs,and it goes back to normal. I run no air lid, a k&n, a hmf sport series slip on muffler, and a aftermarket cdi. I jetted the carb to 165 main and a 42 pilot jet. I put a dif. needle in it and went one knotch down from orig.. What do you think the problem is? Is my main jet to small? I have not done a plug check yet when it does this. I will soon. As long as im not WOT for a while, it runs flawless. Any suggestions would be great,
thanks
Nick(njrextreme)
 

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Discussion Starter · #3 ·
I would say the Main! It controls the wide open throttle.
Did it just start this or has it always done this or have you done another mod to it ????
Its started doing it when i put the hmf on. I went by what they said to jet to, but have a small prob..
 

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Discussion Starter · #4 ·
What should I try? a 170 main? Should I put the needle back to the stock setting?
 

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I would try the 170 aswell. It could also be due to the cold weather. I have a stock pipe with a K&N and lid still on. I rejet mine for the cold. Up the main from a 148 to a 150. Not much but it helps. I also readjust my pilot screw.
 

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Discussion Starter · #7 · (Edited)
I would try the 170 aswell. It could also be due to the cold weather. I have a stock pipe with a K&N and lid still on. I rejet mine for the cold. Up the main from a 148 to a 150. Not much but it helps. I also readjust my pilot screw.
Put a bigger pilot jet in for that. The weather/ cold doesnt make much diff with mine. I choke it, let it warm up for a couple mins, turn the choke off and its good to go. I would look into a pipe and a cdi for yours. It will wake up your quad big time. The couple benifits I saw were gain in rpm, and I can start it in reverse"great for the woods". I just need the bigger main I would think and Ill go from there. Or I may just upgrade to a aftermarket bigger mm. carb. The way mine is set up, it pulls on the more mod'ed 400's in my group. Mine is the head of pack. Even in front of the big bore 400. He has more top end, but I out drag him every time.
 

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I want a Sparks Exhaust. I ride with my 7 year old and he rides a 50 dirt bike and It keeps my quad quiet so I can here him around me. When he upgrades to something bigger I will get my Sparks!!
 

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Hi, new here. I have a 05 400 ex w/ a few small mods and having a problem when WOT.:confused: It runs great all other times.

If im toped out in fifth and WOT for a little while, it will begin to
cutouts like its running out of gas. If I pull the clutch and give it a few revs,and it goes back to normal. I run no air lid, a k&n, a hmf sport series slip on muffler, and a aftermarket cdi. I jetted the carb to 165 main and a 42 pilot jet. I put a dif. needle in it and went one knotch down from orig.. What do you think the problem is? Is my main jet to small? I have not done a plug check yet when it does this. I will soon. As long as im not WOT for a while, it runs flawless. Any suggestions would be great,
thanks

Nick(njrextreme)
ive been looking for some cutout pipes.. can you send me or recommend me some store to purchase it? thanks a lot.
 

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If you haven't solved your problem yet, try a smaller main jet (down 2 or 4 sizes) - kinda sounds like its loading up - pulling in the clutch and revving it blows out some of the carbon and it runs good till loaded up again. Or maybe might try a one step hotter plug. It will raise the temp of the tip of the plug (when fully warmed up) about 5 degrees.
 

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This maybe a dumb question but...can I assume we are talking Keihin jets and NOT dynojets for the main jet considering they are different numbering systems?
 

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No - I am talking about jets. I could care less about who's jets or what numbering system. A specific size hole lets a specific amount of fuel through it regardless of what number is is on it. If the mixture is too rich, you need to decrease the amount of fuel. I always change in steps of two to save time. Perhaps Dynojet has double the size choices than Keihin or Mikuni which means you will have to go down more size numbers till you get to the right mixture. If this were the case, you would get to the right mixture more quickly when using OEM jets versus using Dynojets and typically a single size change is undetectable to a tuner. Go down in two size increments till it runs cleanly then go back up one if you want to.
 
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