over heating

[sportrax stu]

hey guys i own a 400ex with a k&n air filter and a fmf powercore4.
i haven't jetted it yet.
i have noticed that my bike is running really really hot and it takes ages to cool down. what do you think it is? do you think that it may be because i havent jetted it?
any help would be wonderful, thanks stu

[300exOH]

Originally posted by sportrax stu
hey guys i own a 400ex with a k&n air filter and a fmf powercore4.
i haven't jetted it yet.
i have noticed that my bike is running really really hot and it takes ages to cool down. what do you think it is? do you think that it may be because i havent jetted it?
any help would be wonderful, thanks stu

Sounds like you just need to rejet. You are probably running dangerously lean since hondas are lean from the factory to begin with. A lean engine will run much hotter than a properly jetted one.

[sportrax stu]

would i have to put the standard jets back on if i put my standard exhaust on?

[300exOH]

Originally posted by sportrax stu
would i have to put the standard jets back on if i put my standard exhaust on?

If you keep the K&N filter you may want to go with one or 2 sizes up from stock on the main jet.

[sportrax stu]

ok thanks. if my bike is running lean would i be able to get away with adjusting the air fuel mixture?

[300exOH]

Originally posted by sportrax stu
ok thanks. if my bike is running lean would i be able to get away with adjusting the air fuel mixture?

Adjusting the air/fuel screw will only adjust your pilot circuit(idle to about 1/4 throttle)

[sportrax stu]

i really have no idea what size jets to go for. fmf recommend 150-152 main jet and a 40 pilot jet. but this is recommended for a temperature of 70 degrees and it certainly aint that warm in england!

[300exOH]

Originally posted by sportrax stu
i really have no idea what size jets to go for. fmf recommend 150-152 main jet and a 40 pilot jet. but this is recommended for a temperature of 70 degrees and it certainly aint that warm in england!

In colder weather you will need a slightly larger jet to compensate for the colder more dense air. Usually 1-2 sizes larger should do the trick. I haven't jetted a 400ex so I can't help you much with jet sizing on it. Maybe someone will chime in with some recommendations. I'm pretty sure the 40 pilot will be okay...it's supposed to help with cold starts. I would go with FMF's suggestion and run it and pull the plug and go from there. The plug should be a nice tan color if your jetting is right. If it is white/chalky then you are still lean. If it is black/wet then you are too rich. You may have to play around with it since there is no real set specs for jetting... it all depends on temperature, riding conditions and elevation.

Nice to see another member on here from "across the pond"!

[sportrax stu]

thanks very much for your help!