KDXRIDER.NET

Do you guys change your jetting from winter to summer and vice versa? Curious...

I'm partly curious because my former sharp running KX is running really poorly on the low end. It ran like a razor during the winter and spring when temps were 50-65 and humdity was 25-35%. I didn't ride much during late spring and then summer hit. Temps are now in the 90's with 50-70% humidity (it's been raining). I've ridden it 2x in the past couple months and it bogs really bad at 0-1/3 throttle. Past 1/3, it comes back to life, but below, it almost wants to die. It feels to me like a lean condition rather than a rich condition. Messing around with it today, I found that it ran better with the air screw closed! That doesn't make sense since with the increased temp and humidity, it should be running richer and I should be opening that air screw, not closing it. I MAY have found the problem- when I went to check the plug, the cap was not on very tight. Lack of spark could make it feel lean. But it's dark now and I won't have a chance to check it until tomorrow.

Anyway, I was just wondering if your KDX/KX jetting changes so much between seasons that the bike runs awful.

P.S. The KDX is running great- just got back from riding it. Ol' Reliable.

Oh yeah- the KX has a fresh top end (2 hrs) and brand new Twin Air filters with No-Toil. It did run great the 1st time I rode it but it was still cool and dry back then.

I change the needle and main to compensate for 1/4 to full throttle when the temps get above 85 vs the winter 45-65 temps. I usually run a DEK/4 and switch to a CEK/3 or /4 along with going down one size is the main. The SSS changes as much as 1/8 for the temp changes as well for the off idle to 1/2 throttle adjustment. I don't change the pilot.

You'll want to go leaner in the bottom part of the carburation range. Pilot air screw and pilot jet are most responsible here.

If I had your KX, I would start by turning the pilot air screw out 1/4 turn to lean the mix at the bottom. If you get past about 2.5 out, change to the next leanest size pilot jet and start over at about 1 turn out. If that helps some and you still want to fiddle, try lowering the needle 1/2 to 1 clip position in the slide. This affects 1/4-3/4 throttle range, and may just give you the snap that you are looking for back. Do one thing at a time to see how it affects it.

you can attempt to fine tune your premix ratio, for example, if you've been running 40:1, try 32:1 to LEAN the mix. It sounds backwards, but it works. Don't forget to throw in a new spark plug. I tried jetting a bike with a fouled plug and got nowhere until I figured that out.

Bailey28 wrote: If I had your KX, I would start by turning the pilot air screw out 1/4 turn to lean the mix at the bottom. If you get past about 2.5 out, change to the next leanest size pilot jet and start over at about 1 turn out. If that helps some

Agree, but go back and read my post- the bike is running better with the air screw all the way IN. That suggests that it needs a FATTER pilot, which doesn't make sense. It should be asking for a leaner pilot- as you suggested.

And don't forget that it was running beautifully 3 months ago and I have not touched the jetting since then. So, something changed. I'm just not sure if the weather would cause that much change or if something else is going on. I'm inclined to think that something else is wrong, not the jetting. I'm getting ready to mix up some fresh gas and go try it out now that I've got the sparkplug cap sitting right. I'm hoping that was the problem. If it was, then I learned something from Ryan!


[EDIT]
Just took it for a spin- it's back to running great again. Betchya the loose spark plug cap was just not giving it enough juice at lower RPM's. Either that or the plug was on the verge of fouling. Whichever, it seems to be back- running crisp off idle and pulling hard past 1/4 throttle. From 1/3 throttle up, it'll pull a power wheelie. Thasss my 125!

And the KDX is running good, too. Man, you get off the 125 on to the KDX and it's like, where did all this low end power come from???? One weird thing that I need to check on the KDX, though, is a squeak that I'm getting on certain jumps- it's very hard to make it happen but on certain unloading jumps there's a distinct "squeak!". I put the bike on a stand and bounced everything and can't find it. Maybe it's the chain slapping against something...

Do a full re-jet. Record air data, and jetting needed to suit in a log. The log will eventually allow you to 'guess' at jetting much better.