02' CR250, seems rich, won't clear out

[Demon Speed]

I just bought an 02' CR250. I noticed that it wouldn't clear out and seemed to be running rich. It sounds like the silencer is stopped up if you know what I mean, doesn't have the a bark that a strong running 250 normally has. Taking a plug reading indicated this also. It has an FMF pipe/silencer but is otherwise stock.

Runnning 32:1 Maxima 927 on 93 octane fuel.

I found the bike had a 400 main jet, needle second position, and pilot 32.5. FMF recommends a 380 main and needle in 3rd position. I moved the needle to the 3rd and tried a 390 jet first, with no real improvement. Then tried a 380, with no improvement. Also pulled the plug after going with this jetting and the plug looked quite oily on the threads and dark brown on the porcelan below the electrode.

Finally I tried moving the needle to the second position which obviously made the bike run lean, ( would start surging and ping when throttle was applied.)

The power valve appears to be working, not sure if adjusted correctly though. I took the cover off and reved it a few times to see if the leave arm moved, which it did.

I haven't had time to look at it again this week, but a compression check is next.

Probably will pull the exhaust off too to look for any obstructions and have a closer look at the power vavle.

Does anyone have any other suggestions?

 

[ellandoh]

put it all back the way it was , start with the air screw, find out if your pilot is good.

 

[ellandoh]

actually try this

Spanky's jetting guide:

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 powerband. 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.
Are you fouling plugs? Many people will tell you all sorts of band-aid fixes, from running less oil, to running a hotter plug. Both are incorrect fixes for plug fouling. It's all in the jetting.
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. Unless the person telling you what jets to use is riding an identical bike, on the exact same track, at the same time, his recommendations are meaningless.
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 rejet 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. Worn reeds will mimic rich jetting, and worn rings will mimic lean jetting.
Before you start the jet testing, install a fresh plug. Set the float level to the proper specs, an incorrect float height will affect your jetting all across the throttle range.
Warm the bike completely, and shut it off.
As already stated, start with the pilot circuit. Turn the airscrew 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 idleing. 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 airscrew for the best response.
Now is the time to determine if you have the correct pilot installed in your carb. The airscrew position determines this for you, making it very simple. If your airscrew 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 airscrew for the fastest idle, it's time to tune the airscrew 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 airscrew 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 airscrew is not a set-it-and-leave-it adjustment. You have to constantly re-adjust the airscrew to compensate for changing outdoor temps and humidity. An airscrew setting that is perfect in the cool morning air will likely be too rich 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.
The slide is also a tuning variable for jetting, but slides are very expensive, and few bikes need different slides, so we won't go into that here.
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.

 

[FruDaddy]

Spanky's jetting guide sure is getting around these days

 

[ellandoh]

Spanky's jetting guide sure is getting around these days

if it aint broke dont fix it ;)

 

[SQUIRLEYMOFO]

Could be so far off on the pilot that the air screw does no good. I had that problem also make sure the float isn't too high.......

 

[motometal]

what's your elevation? if you are zero to 1000 ft, in my opinion you need a leaner pilot. A 25 or the next one up (27.5 or 28, whatever they call it). I'm betting that's at least part of your issue. Are you giving it a fair chance to really clear out? Most 250s will condense premix oil in the crankcase, and once the bike starts warming up it takes a bit of wide open throttle to really clear this out. Hoping you have a wide open area for testing. Careful with that leaner main jet/needle. To be safe, you should be running at least half race fuel of some sort. Pinging bad.

 

[dimitri]

on my 02 i just went with a leaner needle. You could try everything the way it is, with the needle in the first position

 

[Demon Speed]

Can't seem to post anything. Kept getting spamkiller, "your post contains one or more links."

 

[john stu]

install an s-8 nozzle

 

[mx547]

or you could use the mx547 method and ditch that crappy mikuni for a keihin--problem solved. mine runs like a scalded ape now (how long's it been since you heard that phrase?)

 

[CR Scott]

A second for the PWK Air Striker...

 

[magneto]

Is the Keihin easier to jet? My Mic always seems to be a little bit off on the low end. Does the Keihin fit well in the existing intake manifold and airbox boot? Any idea how much the conversion would cost?

 

[Faded]

Click Here for the low down on the Keihin.

 

[magneto]

Thanks!