hmf slip on and jetting

[zfrank07]

i got a hmf sport slip on for my 07 400ex...just have a UNI filter ..and the pipe... what jets do i need....I am located in kentucky...I dont know much about jetting carb

[F-16Guy]

I would go with a 42 pilot w/ fuel screw about 2 1/2 turns out, and a 150-152 main.

[zfrank07]

what are the stock jets for this atv?

[Sanddraging28]

what part of Kentucky, i am in maysville...about an hour north of Lexington.....

stock jets are a 148 main jet and a 38 pilot jet


i would try a 42 pilot and a 152 main jet
air screw out 2 1/4 turns........
its been a long time since i had a 400ex that needed jets that small......trying to work off memory

need any more help send me a PM...always willing to help a fellow Kentucky boy

[zfrank07]

i am about an hour south of lexington....just north or somerset. I got a 155 main in right now and it runs good except for idle. it seems to die every now and then....the 42 pilot would cure that problem wouldnt it?

[Sanddraging28]

thats cool....my mom lives in russel springs.

yeh the bigger pilot will help the idle

[F-16Guy]

Jets are cheap, so my advice is:
If you're going to buy a 42 pilot, go ahead and spring for 150, 152, and 158 main jets, too. Try the 152 first, and if you notice improvement in the 3/4 to wide-open-throttle area, go down to the 150, and keep going leaner until it doesn't improve or gets worse. When you notice no improvement or it gets worse, go back to the next richer jet and stick with that. If it immediately gets worse with the 152, it's already too lean, and you need to go back to the 155, and consider trying the 158 to see if it gets better. Again, you'd want to keep going up a size until you see no improvement, and then go back to the next leaner jet.

That is for the main jet, and the improvements should be felt in the 3/4 to WOT range, since that's what the main jet controls. Once you select the correct main jet, you'll want to tune the 1/4 to 3/4 range with the needle. The stock position is probably fine for the mods you have, but you could raise or lower the clip one slot to see how it affects throttle response if you're curious.

Finally, with a 42 pilot, you'll just have to play with the fuel screw until the idle is stable and the throttle response off the bottom is crisp.

It sounds like a lot, but you can change the main jet without even loosening the carb, so at the very least, do that. You don't want to run an air-cooled engine too lean.

[zfrank07]

yes i have got the main jet at a 155 and it seems to run great...but i need to get the 42 pilot in...i have stripped the screw in the clamp to the intake boot. any ideas on how to get it off so i can turn the carb and get to the pilot?