50/50 chance?

[liv4raceday007]

I apologize if this is a topic that is often brought up, but I just want a quick answer if there is one.

I have a 2007 400ex with somewhere around 20 hours on it. It is 100% stock. no mods.

However I have a HMF slip on pipe that I got about a year ago, just haven't put it on. (not sure about jetting) This weekend however, I want to put it on. What are the chances I will need to rejet? Is it absolutely necessary, or wont I be able to tell till after I run the quad with the pipe on for a while? I have the jet kit, but if I don't need to use it I wont.

So what do you think? Is there a chance that I wouldn't need to rejet?

Thanks!

[01boneless]

ask yourself this do you want to get the max hp out of your quad ? do you want to take a chance of overheating or to rich? ID say if you got the jet kit why not rejet lol steve and cjm will give ya a good place to start

[finsteratv]

for just a slip on throw in a 150 main, your pilot should be fine.

[AtvKid4Eva]

You will definitely have to rejet. If you go to HMF's website they give you jetting starting points as far as your main jet goes. They are pretty close. Heres what they recommend right off their site...

HMF Recommended Jetting for 400EX (99-10) 1999-2009: Slip On: 165/170 Keihin Hex

Ive always had good luck with a 165 main and no air box lid.

[finsteratv]

My big gun full and sparks filter is at 160 main..hows a slipon without a lid at 165 :huh just wonderinn

[AtvKid4Eva]

haha this is where i leave this thread because i see a huge debate coming. Ive always rang 165ish on a slip on and 180ish on a full system. Always run perfect. Have fun guys lol

[426kidz]

X2

[CJM]

Depends on elevation and temperature. I have a 170 main and 42 pilot with a worked 416-but Im very close to sea level.

Id start with a 155 and take it down from there.

[trxPOWER]

well it really sounds like your scared out of your wit to take this carb apart and jet it. carbs are not that hard to figure out, but if your honestly that scared to do it, mabe just beter to take it to somebody and have them jet it in for you.