'05 YZ250 too rich??

[walnish]

I bought an '05 250 2 weeks ago and broke it in properly, and I fouled 2 plugs in my 1st 2 days out and both were wet and fouled badly. Sunday, I raced a H.S. and the YZ ran flawlessly and started first kick the couple of times I stalled it. After the race I checked the plug and it was covered in oil. I am running Yamalube at 40:1 and stock jetting. Most of the race was tight low speed stuff, so I never really opened it up for any long periods. I was going to back out the pilot air screw a few more turns and go down to a 48 Pilot if that doesn't work. Any help would be appreciated. I am coming off of a '94 XR600 to this YZ, and what a difference!!! I love the bike, I just need to get the carb right. I love this 2-Stroke.Thanks, Walt

[scooter842]

Sweet another 05 yz 250er Welcome to ATM and also welcome to TEAM YAMAHA lol.. here is what i go by when i jet my bike. I too have the same bike you have and i LOVE IT. better than any other bike ive owned or ridden. What have you done to yours? anyways here is the steps that should help you with your jetting prob.....
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 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 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 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 neccessary 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 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 begine 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, ansd 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.

[walnish]

Thanks man I'll get on it. Any tips on the easiest way to change the pilot jet. I have loosened the bands and rotated the carb, with no luck. Does the carb have to be removed entirely for a jet change? Any tips on my easiest way to get it done? . I love the YZ. I just need to get the carb dialed in and I'll be even better. Thanks, Walt

[scooter842]

Ah man thats the hard part.. Pretty sure you have to take the carb off to take the float bowl to get the pilot out. Thas what i do anyways. You might be able to shift the carb enought to get the bowl off. Might have to losen the clamp that holds the throttle tube to the frame. Let me know what you find.

[teknition1]

To get the pilot jet changed.....remove the seat bolts an take the seat off....at the rear of the gas tank there is a long bolt and nut...remove it....loosen the rear hose clamp on the carb....follow the 2 aluminum bars down at the rear of the bike....there is a bolt in each side at the bottom of the bars...remove those 2 bolts ..now gently wiggle the whole back end, fender and all....it will come off.....that piece is called the removable sub frame...once you have that off ,set it aside....now loosen the hose clamp at the front of the carb...wiggle the carb out of the boot and you will have enough room to take it out the left side of the bike and turn it upside down without removing the throttle cable....remove the 4 screws that hold the float bowl on the bottom of the carb.....you will now be able to get at your pilot jet and main jet...while you are there check the float height with the spec in your manual that you got with the bike. Yamaha made an excellent manual for the bike...i suggest reading it cover to cover in your spare time .....lotsa good info in there

When you go to put your subframe back together make sure the muffler pipe goes into the exhaust pipe rubber properly.

Once you take the subframe off once you'll see it is a fairly easy task to get at the carb and wont take long at all the second time around

[scooter842]

^^^^^^^^^^^^^^^^^ nice work

[teknition1]

Thanks Scooter

[Satch0922]

great thread you guys!

[walnish]

Thanks for all of the great info. I am coming from a '94 XR600 and Thumpertalk over to an '05 YZ250 and AllThingsMoto, and I love the YZ and ATM. You could imagine the difference in weight alone. I love my XR and plan on keeping it. I rode the 600 in many Hare scrambles and I ran my first on the YZ250 this past Sunday and I had a blast. What a bike!! I was much less beat up and worn out as well. Some of the real steep hills that were slick were a beast with the XR. With the YZ, I just kicked it down a gear and flew to the top, bouncing off the rocks on the way up and even stalled it part of the way up one hill, and held the brakes, kept my balance, and was able to kick it over real quick and race on. With the big 4-stroke I had to find TDC and give it a good kick while trying to keep the beast upright and still. Keep the advice and tips coming. I have ridden, but have not owned a 2-stroke since my '82 RM80 when I was 12 yrs. old. What's up with Pingertalk? It looks like they get a post a week Thanks again, Walt

[teknition1]

Welcome back to the 2stroke world

[ivesdj]

great post.

gotta get the yz250 rolling hard again.

[walnish]

TEKNITION1, Thanks for the subframe info. I took it off with no problem and changed out the pilot jet from a #50 to a #48 and I rode 50 miles Sat. and it is now running leaner, but I need to go down on the Main as well. It's amazing how easy it is to get the subframe off. I did notice that I was getting some pre-mix goo coming from where the exhaust comes together. I guess it wasn't seated properly. I just took it off again a frew minutes ago and I'm getting ready to change the main jet. It also makes for easier cleaning of the rear of the bike. Thanks again for the info. You're right that the manual is full of all kinds of info. Walt

[RaptorRacer888]

Yea I had a problem with my 250 being too rich from the factory too, changed premix and leaned it out with the air screw and its good now. I should drop my pilot down to a 48, but I think its good as it is now.

[walnish]

When you say that you changed pre-mix, what were you using and what did you change to?? Walt

[scooter842]

Hey Walt, glad to hear you got your bike running better. I know mine had lots of hidden power before i got it right finaly, sure makes a diffrence.

[halfabee]

I am also trying to get my YZ250 05 jetting perfect. I have gone down to a 48 pilot, 172 main. Only thing i havn't changed is the needle setting. Even after going down to a 172, 48 with the air screw out about 1,5 turns i am still getting loads of goo comming out the exhaust.
Should i play arround with the needle settings or turn the air screw out some more? i stay at about 5750 ft (1753 m) above sea level.
I really want o try and work this out myself and not send it to someone to do it, gotta work this out someday.

[Budlite]

take the subframe off to rejet ??? I really don't think so...and I have one too

[khyz250]

Halfabee...

Make sure you change your packing in your silencer after you jet your bike.
The spooge you are getting may be from your current packing being saturated.
I would also suggest raising the clip on the needle.

khyz250

[halfabee]

i did have brand new exhaust packing in when i started re-jetting. Moved the needle clip up 1 position (now right at the top). I don't get as much sploog comming out the exhaust now but still get quite a fair amount. Will keep trying to get it perfect. Any other sugestions would be cool, don't want to go any leaner on the main, should i try a leaner needle maybe ? I did notice that the sploog seems to be thinner (runny) than before, before it was thick blobs of goo. Does this mean that i am on the right track and getting the jetting leaner?