man the ole 2001 DR-Z250 gets no love in the jetting forum...

I have opened the airbox

uncorked the exhaust

richened the mix a little (about .75 turns from stock)

could go more I think

but now I'm getting the idle coming up all by itself

I can kick it down with a hard twist of the throttle

but then it comes right back up again

any thoughts?

is this a float bowl issue?

would this happen if I have maybe installed the carb out of plumb?


First thing to check is the throttle cable itself. See if this idle speed change occurs when you turn the handlebars hard left or right. I have had the cable tighten up after I worked on a bike by fouling up the normal cable routing. If it was lean mixture, the high idle would be a surging on-off thing.

ah good point.

I did just install higher handle bars.

i did also have cable problems before the new higher handlebars but fixed that a while ago with cable lube. the throttle was sticking.

also the the previous owner or maybe a mechanic had the throttle cables routed up and over the brake line. I fixed this.

I'll double check to see if turning the handle bars revs the throttle.

thanks glenn!

Hey wolffo1 did you end up sorting out your high idle issues?

I have a DRZ i bought cheap, that has had a hard life and the slide is really worn. i think this is causing the idle to rise because air is getting sucked past the worn parts.

Anyway I have order a tm33 carb. should be here any day now.

Anyone else know if stock jetting in the 33 is good or does it need to be richer because it has more air flow?

If the idle kicks down, but then rises up again, it could be the cables, but it might also be that the pilot system is too lean.

The pilot system dominates the mixture setting from closed throttle up to about 1/4 open. The pilot system consists of the pilot jet and the pilot screw. The screw is the fine tuning. Turning it out (CCW) richens the mixture. If the best setting for the screw is all the way in (CW), then the jet needs to go down one size. If the best setting for the screw is more than 3 turns out, then the jet needs to go up one size.

I adjust the pilot with the "quick return to idle" test. Rev the engine up and cut the throttle. If it drops down to a consistent idle, then it is good. If it hunts around before dropping down, or never drops, then it needs to be richened. If you need to richen it, turn the screw out and repeat the test. The leanest setting for which you get a good return to idle is what you want. If the screw gets more than 3 turns out and the return to idle is still not good, then you need to go up one size on the pilot jet.

You mentioned that you opened up the airbox. I have found that sometimes opening up the airbox leans out the mixture at idle. That is good... less restriction on the intake side is a good thing. However, sometimes a readjustment is needed. In my opinion, making a modification to the intake or exhaust tracts should make a difference. If it doesn't, then it should be questioned whether it was making any difference. The fact that you may need some jetting adjustment after opening up the intake, is an indication that your airbox mods made a real difference.

nope mine still idles up

I can kick it down but it'll come back up

I've richened the mix a lot but its still has the problem

it runs pretty good though even with this problem

I have the dynojet kit sitting in my garage.

I'll get to it soon, but with the bike running pretty dang good right now I'm not in a huge hurry to tear it apart and potential have lots of little trouble shooting problems to deal with on that.

I'll probably get to it over then next 3 weeks or so

but right now its time to ride!

I've richened the mix a lot but its still has the problem

How did you richen the mix a lot?

Wolffo have you pulled the slide out of yours yet?

If your bikes an older one like my 02, than you may have a severly worn slide. this lets more air in making it lean. My bike has 40PJ and the mixture screw is still 4 turns out and i get high idle.

Thats why i bought the TM33 carb, it was either that or a jet kit and a new slide, which was about half the price of the upgraded carb

I don't know what the slide is

I have opened the mix screw 1 and 1/4 over the stock setting

and I think I could prob richen it more

it still back fires a little but its a diff kind of back fire than before openeing up the mix screw now its more of a gurggling type of backfire, before it was a hot popping sound

The pilot screw is just the fine tuning of the pilot system. Opening it up is, most likely, given the mods that you have made, a step in the right direction. However, if it is more than three turns out, opening it up more will not have much of an effect. At that point the pilot jet needs to be replaced with the next size larger. This entails removing the carb, taking off the float bowl and replacing the jet. It is a very straightforward process. If your bike has the Mikuni TM28P carb (non-California model), then it came with a 37.5 pilot jet. You need to install a 40.

I usually take the jet to my local dealer, just to be sure they get the right one. They almost always have a good supply of Mikuni jets on hand. If you are in the Colorado Springs area, I might have one handy in my supply of jets.

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