2006 CRF250x Carburetor Jetting Questions - pictures!

I recently picked up a 2006 crf, and the guy i bought it from BOTCHED the jetting. I've never heard a bike run so rich! First thing i did when i got it off the trailer was pull apart the carb. Like i suspected, it was jetted really rich. (162 Main!)

I've been reading up, and getting the facts about what jets to use. However i'm having trouble identifying What's What!


The jet in the middle with a hex head is the main, The one above it between the idle mixture screw and the main is the piolt jet.

The other jet (i don't know what it call) you will likely never touch it. The leak jet is in the fuel bowl.

I dont know what mods have been done to it but im running a 165 main and and my buddys bike is running a 168 main. Both bike are on the lean side at sea level. Both bike have all the ccc mods, 05 r cams, and the exhaust has been changed.

That main jet may not be as lean as you think.


My bike has the 'r' cams as well as an aftermarket exhaust and K&N air filter.

The needle is definitely stock, as for the other jets, i'm not sure what size they are. Will post those when i get home.

Could my bike be running lean? I know it is possible to get the "pop" if the jetting is too lean or too rich.

When i pulled the spark plug, it was black and dirty which is why i think it's running rich.

Am i right? What would you suggest for jetting at sea level?

I looked into a dynojet kit and the largest main jet they provided in the kit was a 132, and 48 pilot jet. Are you sure 160-170 is normal for the main?

The bike that is running the 168 main has an 05 r cam, air box cut open to the line, stock air filter and screen, honda piston, RHC valves, stock X head pipe, 04 r muffler with an PMB end cap. Bike was running a R head pipe but changed it to the x head pipe last saturday.

Figured i should jet it down a little too and went to a 165 main

The bike would start to sputter at 3/4 and above throttle. Switch main to a 162 and it got worse. Went back to a 168 and its back to pulling hard.

I would think the 140 size jets would be fine for stock exhaust, cam and/or air box not cut. I think i was running a 145 main back with the air box cut, stock cam, r head pipe, and stock pipe.

Look up what dyno jet is running for r bikes.

Easy way to find out is get a 165 main and a 155. See witch one it like the best. Should be obvious.

Both bikes also run a 45 pilot. Main reason is so my t handle mixture screw doesn't want to vibrate out at only 1/2 a turn.

dyno jet uses there own sizing numbering, not comparable to keihin numbers. Their kit also is calibrated with their needle and what ever airbox mods, if any, they say. Also pipe mods.

Some of the main sizing you'll find posted here is from the JD jet kit, which also uses thier (generic) red or blue needle which has a fat tip, so uses a bigger jet. Same with the R needle spec'd in the CCC mod calibration. If your jetting with the stock X needle you might find you'll be a little smaller on the main.

Suggest jetting in steps of 5.

I'm pretty sure dynojet sizing is the same as keihin.

the jets provided with the 2006 'r' kit range from 150 to 170.

I know the dynojet needles are tapered differently than the stock needle, which could be why the jets are smaller. but i'm not sure, my bike is modded enough from stock that i'll probably have to play around with the jetting a little bit to find out what works.

Does a dark spark plug mean you're running too rich, or too lean?

Depending on the mods, the 162 may be good as mentioned before. Dont be fooled by the popping on decel on these bikes. The air pump will make it pop even when jetted perfectly. That is perfectly normal. My bike is an 04 250X with CCC mods, 06 R cam, R pipe and silencer with a pmb spark arrester..I ride at around 400 feet altitude. I am running a 165 main, stock needle, 42 pilot, 55 leak. When warmed up bike works flawlessly..And yes it does pop on decel. I live in CA so removing the smog pump is not an option.

usually rich, unless what your seeing is carbon from oil burning (past the thin rings, or through the crankcase breather vented to the airbox), where is the color change on the ground strap?

does it run rich on the main? popping on closed throttle decel has nothing to do with the main jet.

To correctly read your plug for your main jet size you need to ride at wide open throttle, kill the bike and then close the throttle.

Your dark plug may only be telling you your bike is idleing rich if the bike is idleing when your shut it off.

dark sooty plug is too rich, bright white is too lean.

Pulling the plug is a pain. use your seat of the pants dyno.

Here are the jets that i'm running

162 main jet.

45 pilot

68 (other jet) slow jet?

fuel mixture screw is 1 1/2 - 2 turns out.

Stock needle


'r' cams

aftermarket exhaust

k&n air filter

opened air box

From what i've been reading, this seems to be an okay setup.

I think the problem is with the pilot circut.

Those of you who have more experience with this... Please comment.

My carb seems to be a little dirty, which might be a contributer to why i'm experiencing some of the obnoxious popping when i roll off the throttle. I'm going to clean it up today, but before i put it back together, i'd like some comments on the jetting.

Dynojet kits are usually a good call.. however the 'x' kit has 118-132 main jets and a 48 pilot jet, which seems really small to me. 'r' kits have 150-170 main jets, no change in pilot jet.

If i were to rejet it would be to get a better needle, and use the dynojet recommendations as a starting point to tweak the jets. Should i consider getting the 'r' kit instead of the 'x' kit?

Pulling the spark plug was actually alot easier on this bike than on my WR450, or DRZ400. all you have to do is take off the seat... and it's right there! Dont have to work around the frame at all.

Edited by drob720

your jetting looks pretty good but I would get that slow jet alot smaller...55 is what seems to be generally accepted as the best choice. The slow jet or leak jet is the orifice that bleeds fuel back to the fuel bowl when the accelerator pump is actuated so the larger the jet the less fuel is injected into the engine and bypassed back to the fuel bowl. So when you go with a smaller leak jet you are increasing your fuel squirt on the accelerator pump

Thanks for the tip.

Will that help with the decel pop at all?

sounds to me like that will make my bike much more punchy when i hit the throttle.

Dont get me wrong..

I'm Definitely gonna switch that out so the bike rips harder when i want it to.

But, Any suggestions for the decel pop?

I was reading some of Eddie's recommendations about tweaking the fuel mixture screw until the pop decreases to a normal amount and - a few on the pilot if the mixture screw is less than 1 turn out, or + if it's greater than 2.5 turns out.

Usually on the 250X the decel pop is a biproduct of the air injection pump. It is normal for these bikes to pop. If you dont have local lawa preventing it, you always put a smog pump block off kit on the bike. That will get rid of the normal pop on decel.

I recently did some mods on my 06 250 x. Opened the air box 4 by 6, k and n air filter. fmf header and exhaust. Used the Jd jet kit set up red marked needle 5th counted from the top grove 165 main jet #42 pilot jet thin O ring. When i start the bike up header pipe gets extremely hot went for a ten minute rip and went into 4th gear and shut off motor coasted to a stop. spark plug seemed a bit whitish? I am no mechanic and looking to problem solve should i try moving the clip down on the needle or go to a 170 main jet which wasnt included in the kit. Im from Vancouver island British Columbia ride at sea level. Cheers

I have a 05 with JD Jetting, partial CCC mods, stock exhaust and ride mostly at sea level in the Puget Sound area.

I don't have the JD Kit with me but my notes show 158M, 42P, red needle, 5th clip position.


These engines are susceptible to intake valve damage from dirt so I wouldn't use a K&N filter because they do not filter as good as a good foam filter.  Also be careful with filter service and the air connection to the carb.



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