DRZ Jetting question

First post on this form, just looking for a few opinions. I bought a 07 S with less than 200 miles, 3x3 air box mod was done, and it has a Two Brothers pipe.

The owner first said it was jetted, then said he just moved the needle clip up.

The Bike starts and runs well, always pops through the pipe on deceleration, sometimes takes a few seconds for the idle to go all the way down.

I tried taped off 1/2 the opening in the air box, that cut the power and lessened the popping when i get off the throttle.

MC mechanic suggested if runs ok to run it till the 600 mile service the check the plug color.

I am wondering if i should pull the carb and see what is in there. Most of all i do not want to do damage to the bike by running it to lean. The bike is a fantastic machine, and i am thoroughly enjoying it.

Any ideas.... Thanks, T

Pull the carb and have a peek. If he said he moved the clip on the needle it would have to be an aftermarket kit, stock needle is non adjustable. Did he sau he adjusted the fuel screw as well? Pull the carb and check your jet sizes. Check to see if he drilled out the brass plug that hides the fuel screw on the bottom of the carb. Stock main is 142.5 I think and pilot is is 22.5 I'm almost positive. I can't remember.

I'll add, 'checking the plug' does nothing with todays pump fuels.. Your 'mechanic' should know that. Find a different one.

Some decel popping is normal with an open pipe. Live with it or get a stock muffler, those are your choices. You should do as 707 says and confirm the fuel screw is properly adjusted (not just set to some arbitrary setting). Also confirm you have no exhaust leaks.

Do not wait to do an oil change till 600 miles. Do it now. Also pull the frame screen this one time and confirm it is clean.

Read the FAQs at the top of the forum to become even more informed.


popping on decel would be unburned fuel in the exhaust gasses with no load - post-cylinder "combustion" if you will. i'd guess it's running slightly rich. although, you CAN NOT get rid of all the popping.

as for the screw - maybe someone can help me as well. just did the jet kit, 3x3, and exhaust, and it runs fine until i REALLY try to get on it. then it's sluggish. is that too rich? if so, which direction do i turn the fuel mixture screw to lean it out a tad? left/lean, right/richen? TIA!

If anything, popping on decel is a lean condition, when you chop the throttle the slide closes and keeps air/fuel from going through the motor.

The fuel screw has nothing to do with engine operation once you get just a little past idle. So turning it won't help you with what you describe. Read this about the fuel screw if you think it needs to be adjusted. http://www.thumpertalk.com/forum/showthread.php?t=327405

Post up what kit you put in, the jets, and what the clip position is, plus exhaust type if you want advice on your jetting.

2009 DRZ400sm

JD jetting, used the red needle as i'm in houston, and it's over 75* nearly 90% of the time. used the 145 main, the supplied other one, with the clip in the recommended location (third from top iirc)

yosh rs2 full



new oem plug


hope this isn't threadjacking - figured it was on par and could help the OP as well. if not, lemme know, or a mod - split it off to its own if you want. :thumbsup:

Thanks for the info/help, I do not think this is being thread jacked as it is similar themes.

Looks like my carb has been "worked on by the PO" as the brass plug is out. Seems not to hard to pull the carb so i will check it out and see what is inside for jets.

Can lean running damage an engine quickly??I am not even sure if is lean or not just the deceleration popping other than that it runs quite well. as i said in the thread starter, putting tape over part of the 3x3 mod lessened the popping, also lessened the zip, or throttle response.

running lean CAN damage a motor. it won't be "quickly" though. lean produces more horsepower, and will ultimately damage engine components b/c it's too hot, too powerful, etc. basically it'll burn it up - at least, that's true for a FI 4 cylinder bike.

running lean CAN damage a motor. it won't be "quickly" though. lean produces more horsepower, and will ultimately damage engine components b/c it's too hot, too powerful, etc. basically it'll burn it up - at least, that's true for a FI 4 cylinder bike.

i rather run a little lean then rich.....these bikes come a little on the lean side from the factory for emissions im pretty sure

as would i. more power is more power. :thumbsup:

you'd be surprised at the difference in feel of an AFR set at 13.5 and 13.0. feels like an extra 2hp. VERY noticable.

and so all you readers know - i'm still looking for advice on my jet selections. :|

....and so all you readers know - i'm still looking for advice on my jet selections. :|

You say the PO jetted it, do you know what jet kit is currently in it? You need to know the brand of needle for people to give you proper advice.

You say the PO jetted it, do you know what jet kit is currently in it? You need to know the brand of needle for people to give you proper advice.

that was the OP that posted that. he hasn't pulled the carb yet. i have a JD jetting kit.

Oops, you're right, sorry for the confusion.

So what did you guys end up with? Seems like all the threads I found when searching for "Jetting Houston" end without every posting the final results.

Guess i am not to good about being current on this stuff.

After some good recommendations I pulled the carb. As expected the P.O had done some tinkering....... some of the screws were buggered up, bellows pinched, fuel screw drilled out . Needle had an adjustable clip, i was told this is not stock?? Stock jets. SO i ordered a JD jet kit, installed as instructed.

Bike runs great, better than before, no popping on deceleration, and seemingly better economy. I have to give the JD A:thumbsup:

Thanks for all your help and and a bit of encouragement, pulling the carb and the bit of wrenching i have done on this bike has been easier than expected.

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