I have an 03 kfx400 and will be installing a pro circuit T4 full system and twin air filter. I will be running with the airbox lid on and no holes in it. Can I just swap main jets or will i have to tune the pilot jet and all that other b.s. as well?? I will be riding at 1100 ft. elevation, what jets should I run???

 

You shouldn't have to mess with the pilot jet, just throw a bigger main jet in it.....I have no idea what size, but you can try a size bigger and keep checking the plug until you know.....or someone else will reply soon....

 

what size is the stock main in your kfx, i went up from a 52 to a 75 with my k&n and hmf slip on.

o ya im at sea level.

 

i believe stock is 142. I have heard guys going as high as 175 on the kfx400 which seems a bit high to me. I was thinking in the area of 160-165 at most. I am mainly concerned with whether or not I can just change the main and leave everything else as is.

 

I also have a Pro Circuit T4 full system.My stock jet was a 134.
I have no airbox lid or snorkel and a K&N filter.I went to a 160 main.
I didn't touch the pilot or needle and it made a huge difference.My elevation is
460 feet above sea level.Since your runnig your airbox lid you shouldn't have
to go too high on the main jet. I would start around 145 or so and do a bunch
of plug checks.A pain in the ars but well worth it when you get it dialed in.Good luck.[img]i/expressions/face-icon-small-smile.gif[/img]

 

My stock main jet was a 135.
Man that pro circuit T4 full system is going to be craveing more air.I would at least drill 3 to 5 one inch holes in the air box lid.If that scares you they make plugs to fit in the holes that are made of the same stuff as the air filter.

 

yeah, i might go ahead and try that then

 

I just installed the pro circuit T4 and head pipe and twin air filter. I started it up and ran it for a bit and it ran fine. Didn't run choppy and didn't sputter. I didn't change the main jet and it seems to be fine. The mechanic at the dealer says that 145 will be as high as I need to go if any. Can anyone help me with this?? What size jet do I need to go to???

 

your mechanic sounds dumb