I recently installed a KDX snorkel, K&N filter, HMF slip-on and did the typical carb mods (#122 main jet, N1TC needle on 2nd slot, and 1.5 turns out on air/fuel screw). After all the mods were done, I've noticed that the bike backfires when I rapidly decelerate from 7000 or 8000 rpm. Is this normal? Could I be too lean? If so, can I fix the problem by adjusting the fuel screw? By the way, I live at over 6000 feet in elevation and its darn cold here right now. Thanks

 

You will hardly notice the bacfiring with the stock exhaust, butyou will definitely notice when you switch tothe HMF. Have you disconnected and plugged-off the smog plumbing yet? That's a big source of back-firing on this bike.

I would think that a pop or two during rapid decel from high RPM is pretty much normal, but you can eliminate as much of it a possible by plugging-off the smog gear andensuring your head pipe has a good seal. Also make sure you've got a good seal on the intake boot after you re-installed the carb after re-jetting.

My bet is that you won't totally elinate the backfiring from a rapid decel, but that's really no big deal.
Good luck.

 

122 main with the snorkle, K&N and a pipe seems lean to me. In fact, the entire jetting seems lean.

 

All of my backfiring from high rpm went away when I removed the smog equipment and put a blockoff plate on the cylinder head. I haven't had a decel pop/gunshot in a long time, just the occasional burble but nowhere near as bad as it was with the smog crap on there.

 

Keep in mind he is at 6000 feet. I don't know if this would still be lean at that altitude, but that's gettin' on up there.

 

Did you change the pilot jet to a #40?
If not you may need to change that and go up to a 125 main (in addition togetting rid of the smog stuff)

Take a look at this thread and compare your setup to members at your elevation.
https://www.kawasakiforums.com/m_67995/tm.htm

 

Ah, didn't notice that.

 

Thanks for the advice everyone. I did not change the pilot jet nor have I removed the smog stuff. Does anyone have a link(with pictures) for the smog mod?

 

I'm sure there is but I just did mine. Take off tank and all becomes clear. Basically cap 3 locations--head, carb & airbox. It injects fresh air in the header to help ignite unburned gases, this can cause a popping even if your bike is not lean. It also does no harm, it just may be an annoyance (to some anyway, sounds mean on my street bike with aftermarket cans).

 

In my case it also heated up the head pipe quite considerably, to the point that brush/leaves would start to smolder if they got stuck on the pipe between it and the heatshield. I haven't had that happen since removing the smog stuff.