I need some help with the main jet on my 400ex. I just put in a K&N High Flow air filter and bought a Dynojet jetting kit. The Dynojet kit recommended a 146 main jet for my quad's setup of an aftermarket exhaust and aftermarket air filter. I tried the 146 main jet, but the exhaust header is getting really hot. I was running a 148 main jet before putting in the new filter, so I'm not too sure what main jet I should use. Any help or suggestions are greatly appreciated!

 

So you had a 148 in there to begin with and you put a 146 in? You went down in jet size even though your putting more air through the engine?

The only reason to run a K&N is to get more air flow to make more HP. Your getting more air flow so you need to richen it up to make up for more air.

Put a 154 in it and see how it runs. Too rich? Go down a size or two at a time.

PS If DJ recomended a 146 and your way lean that is a good thing. For some reason your engine is pushing a lot of air through it.......way more than DJ thinks you should. That means your making lot of power.

Good luck and let us know how it turns out.

 

I was kinda confused too about going down in jet size too, just thought I'd follow the recommended setup. I'll throw the 154 main in it tomorrow and see how that goes. Thanks for the help.

 

No problem.

Keep in mind that DJ only has recomendations. They can't know all the parameters of your engine or the conditions it's under.

Like I said; let us know. It's going to haul a$$ if it takes that big of a jet.

 

I put in the 154 main jet and it fixed the issue with the overheating, but I'm getting some bog right when I shift gears. I also tried to pin it in neutral just to see how it ran, and it sputters at full throttle. Thanks again for the help.

 

put the 146 back in , turn your air fuel screw out one full turn .... try that ...

 

I have the 150 main in now and its running great, no overheating at all. I'm just having the bog when I shift now, any idea how to fix that?

 

If it's a bog raise the clip one slot and see if that helps. This will lean out the mid range a bit. A bog (over rich) is hard to tell from a lean mixture. Sounds like your getting close.

 

The mid range is alright, it only bogs when I reach the top of the gear and go to shift. The engine stalls down for a split second, and then it just keeps on going into the next gear. Also when I had it in neutral and revved to full throttle, it revs up, dies down, and revs up again. Any idea on the cause of that or if moving the needle will help that also? Thanks again.

 

I was also just reading that the stock main jet is a Keihin 148, and Dynojet uses a different sizing chart for their main jets. I believe it says that the stock 148 is equivalent to the 134 Dynojet. So that means that the 150 main I have in now would be somewhere around the 165 main jet for Keihin?