hmf exhaust (which jet do i need)

[DIRTRIDER22]

i have a pretty much stock 2007 400ex. I just installed a hmf sport series slip on pipe,which by the way i am very pleased with. I know i am supposed to rejet and was wondering what size comes stock and what size i need now. also will i need to rejet again when i get an air filter? thanks guys.

[dang400ex]

It all depends on your elevation. Stock size is a 148 Keihen main jet and 38 Keihen pilot jet. I first put in a 155 K main jet and 42 K pilot jet (for easier starts) when I installed my HMF sport series and UNI filter. It seemed a little too rich to me and bogged down and popped on deceleration. SO. I replaced the 155K MJ with a 152K main jet and it runs almost perfect I would say but might be a little lean. I am at 800 ft above sea level I think.

[DIRTRIDER22]

Thanks man, I talked to a gut who has been racing for 35yrs today and he said that i really dont have to rejet,untill i get a intake and filter? He seemed to know quite a bit.

[RaginRedneck]

DirtRider22,
You're going to want to rejet with the slip on. Jets are cheap if you buy them individually, or break down and buy a kit if you plan on making several changes over time, and install is pretty simple.

Also if you look on the first page of the 400EX section someone started a thread to list what mods everyone has, the jets they are running, and the elevation/temperature that they are at in order to answer this exact question. We are hoping that it will get a "sticky" and will sit at the top of the page for a good reference point. You may want to take a look at that, there are only a few replies right now, but I'm sure the list will grow and it should give you a good starting point.