quick jet question

So i've done a bunch of searches and seem to come up with conflicting info or info on different model years...... So just wondering if i could get some quick info.

What is the proper jetting for:


RM 265

Full PC exhaust

32:1 fuel mixture.

Thanks, i know that you guys get a million jetting questions.

Oh, and the reason i ask is because i've never owned a 2 stroke before and i have no idea how a properly jetted 2T runs compared to one that isn't.

the last time i rode it was a little hard to start, i don't know if that was because of a fresh top end or the cold or poor jetting.


all I can tell you is the stock jetting for an 05 RM250:


And PC recommends these settings with PC exhaust, again for the 250:



NECJ, 3rd

air screw 1 turn

power jet 45

slide 7.0

I don't know what it would be for the 265, but all bikes are different, so I'd recommend reading through this jetting FAQ it's a good way to get a handle on jetting, it's pretty easy once you get into it:


Good luck!

Maybe my question would be better answered if i asked how do i know if it's running lean, rich, or right on?????

i appologize but i know absolutely nothing about 2 stroke jetting.

OH, and why would PC recommend leaner jets? doesn't the exhaust system add more air which would make the bike run leaner? or is that only in 4 strokes?

2006 RM 250



Needle: NECJ

Needle Clip:3

Air screw:1 turn out

Power Jet:45 (45 is probably the stock size)

Slide: 7.0 (also probly stock)

These are Pro Circuits jet specs. I would assume these are baseline specs at sea level and 32;1 mix.

Maybe my question would be better answered if i asked how do i know if it's running lean, rich, or right on?????

i appologize but i know absolutely nothing about 2 stroke jetting.

I tried to find some good photos of some spark plugs to show you what a good jet set up should look like and also some photos of jetting conditions and what to look for. However, google let me down. I know on TT there is some threads over this subject, but I could not find them in my search. Sorry I tried.

What your shooting for is a nice coco brown center on your plug. Now even if it comes out coco brown, you need to pick out if it a dry coco brown (your close, but need to go up one more step on the main) or does it come out a wet coco brown (again close, but now we need to drop it just a little bit). Your plug should look coco brown (I know I said that already) but should have a very light glossy look to it. Now your on the money.

For the pilot jet, I really like to drop the jetting about 1 step lower than stock. I look for a clean ideal and crisp throttle responds when I blip the throttle. Bike runs clean out of the corners and wont load up on the starting gate.

I ride MX and do not ride trails very much at all (trees move on me). I do jet my bikes just a little on the rich side. We ride in deep sand most of the time and it really wears the bikes down. If your jetting for trails then I am not your man. I just cant set one up that lean.

OH, and why would PC recommend leaner jets? doesn't the exhaust system add more air which would make the bike run leaner? or is that only in 4 strokes?

Correct on the more air pull, but with more air comes more fuel. In other words with more volume of air being forced threw the carb, the more fuel is metered into the mix. So leaning down on the main for sure is required to compensate for the increased volume of flow produced by the new pipe.

Thanks to all so far, now i feel like i'm getting somewhere. i know these things are hard to just explain on a message board but i'm kind of flying blind and any assistance is very helpful.

maybe i'll pull my plug and take a picture and i can get some comments on that.

Yal, read the link posted above and anything else you can find on the net. I know in the general forum there was a guy cutting up spark plugs on a 125 and had photos of plug conditions, but I could not find it. Once you learn how to read a plug and understand how a two stroke carb works, then jetting is easy as long as the top end is in good shape and no motor problems. When you understand it, you will be jetting like a pro. Good luck.

I found this in my notes. Sounds alot like the link you posted.

Throttle Ranges:

Pilot Jet/air screw:0-1/4.

Needle Jet:1/4-3/4

Main Jet: 3/4-Full open

A correctly jetted carb makes a tremendous difference in the torque, midrange pull, top-end pull, and over-rev of your engine. If you have never jetted your bike correctly, you will almost certainly gain some performance at some point in the bike's power band. A cleanly jetted pilot circuit can be the difference between having to clutch the bike out of a turn or not. The needle can make all the difference in the world for the power of the machine in most situations, as it controls the throttle range that most riders spend most of their time using. A correctly sized main jet could mean the difference between being able to rev out high enough to not have to shift one more time at the end of the straight, or the power falling flat on top and requiring you to make that extra shift.

The only way to know what jetting changes you will need is by trial-and-error. No one can give you jetting specs, because every bike is different, every rider has a different style, and jetting is totally weather dependent.

Jetting is fairly simple, and is a useful skill to learn if you ride a two-stroke and want it to perform at it's best.

It's very important that you start with the pilot circuit. The reason is simple. The pilot circuit affects the entire throttle range. When you are at full throttle, the main jet is the primary fuel metering device, but the pilot is still delivering fuel as well, adding to the total amount of fuel that your engine is receiving.

Before you start to re-jet your bike, you need a clean air filter, a fresh plug (actually you need several plugs to do plug-chop tests for the main jet), and fresh fuel. One important detail: Make sure the engine is in good mechanical condition. If your engine has a worn top-end, fix it first. Trying to jet a worn out engine is a waste of time. The same goes for reeds that don't seal properly, and a silencer that needs re-packing.

Before you start the jet testing, Install a fresh plug. Warm the bike completely, and shut it off.

As already stated, start with the pilot circuit. Turn the air screw all the way in, then turn it out 1.5 turns to start. Start the engine, and turn the idle screw in until you get a slightly fast idle, or hold the throttle just barely cracked, to keep the engine idling. Turn the airscrew slowly in, and then out, until you find the point where the idle is fastest. Stop there. Do not open the screw any farther, or your throttle response will be flat and mushy, and the bike may even bog. This is only the starting point, we will still have to tune the air screw for the best response.

Now is the time to determine if you have the correct pilot installed in your carb. The air screw position determines this for you, making it very simple. If your air screw is less than 1 turn from closed, you need a larger pilot jet. If it is more than 2.5 turns from closed, you need a smaller pilot jet.

Once you have determined (and installed it if it's necessary to change it) the correct pilot jet size, and tuned the air screw for the fastest idle, it's time to tune the air screw for the best throttle response. Again, make sure the bike is at full operating temperature. Set the idle back down (the bike should still idle, despite what you read in the Moto Tabloids), and ride the bike, using closed-to-1/4 throttle transitions. Turn the air screw slightly in either direction until you find the point that gives you the best response when cracking the throttle open. Most bikes are sensitive to changes as small as 1/8 of a turn.

The air screw is not a set-it-and-leave-it adjustment. You have to constantly re-adjust the air screw to compensate for changing outdoor temps and humidity. An air screw setting that is perfect in the cool morning air will likely be too lean in the heat of the mid-day.

Now, it's time to work on the needle. Mark the throttle grip at 1/4 and 3/4 openings. Ride the bike between these two marks. If the bike bogs for a second before responding to throttle, lower the clip (raising the needle) a notch at a time until the engine picks up smoothly. If the bike sputters or sounds rough when giving it throttle, raise the clip (lowering the needle) until it runs cleanly. There isn't really any way to test the needle other than by feel, but it's usually quite obvious when it's right or wrong.

Last is the main jet. The main jet affects from 1/2 to full throttle. The easiest way to test it is to do a throttle-chop test. With the bike fully warmed up, find a long straight, and install a fresh plug. Start the engine, and do a full-throttle run down the straight, through all gears. As soon as the bike tops out, pull the clutch in, and kill the engine, coasting to a stop. Remove the plug, and look deep down inside the threads, at the base of the insulator. If it is white or gray, the main is too lean. If it is dark brown or black, the main is too rich. The correct color is a medium-dark mocha brown or tan.

Once you have a little bit of experience with jetting changes, and you start to learn the difference in feel between "rich" and "lean", you'll begin to learn, just from the sound of the exhaust and the feel of the power, not only if the bike is running rich or lean, but even which one of the carb circuits is the culprit.

Keep in mind, even though this article is intended primarily for two-strokes, four-strokes also need proper jetting to perform right, although they are not quite as fussy as their oil-burning cousins. The only real difference in the two is with the pilot circuit. Two-strokes have an air screw that you screw in to make the jetting richer, and screw out to make the jetting leaner. Four-strokes, on the other hand, have a fuel adjustment screw that you screw in to make the jetting leaner, and out to make it richer.

Edited by Padgett
Found some info

ok so i finally got a chance to dig into my carb and it is jetted exactly as you all have said that PC recommends.

Needle - necj 3rd clip

main- 168

pilot/slow- 48

power- 45

slide- 7

So i either way i should be close. next i'll get ahold of PC and see if the recommend anything different for a big bore engine. a couple people have said that with a BB kit you need to go a couple richer on the main jet.

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