Help - Fouling Plugs

[Rodp]

Hello, I just recently bought a brand new Yamaha YZ125. For break in they told me to mix premium gas 15:1....for a few short half throttle runs....stoping to let it cool in between. Then crack it open for a short run. Drain the fuel and the refill with 30:1. Did that a I have only had about 16 hours use and have gone through 4 plugs. Fouled wet oily black . Is this normal??? B9EG is the recommended plug. I do some trail riding but I am always cracking it open. Yamalube I was told for the break in and then Belray for the life. Will I always have to carry a plug wrench and screwdriver? Will using a BR9ES make any difference? Do I mix the fuel-oil mixture leaner...say 35:1. Can this prematurely wear the engine? Need help. Thanks.
Rod

 

[moabdaze]

When you check your plugs, do you do a hot burn? Or is it possible you've been shutting down from idle and then checking. Let us know, and we can probably give you more info. And yes, running your mix leaner than factory rec's may lead to more wear. The operative word is may. But if you're running to rich to begin with.....................

 

[ellandoh]

everyone has an opinion on oil and ratio i see most people around here use either 32;1 or 40;1 and always use the same kind even for break in and jet for your mix NOT mix for your jets here is my personal favorite jetting help i will paste it here for you


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.

 

[topher04r1]

you are running a BR9EG plug ? .... seems to me that you may be able to go to a BR8EG or ES depending on how much coin your willing to shell out. only thing between the to i believe is that the ES has an extended tip electrode and cost's a few cents more.

" I do some trail riding"

what kind of trail riding ..... are you just putting along or are you staying in the power band constantly ? how agressive are we talkin bout ? ..... if your just puttin along and not riding all that hard i immagine that a warmer plug wouldn't be a problem .... :cool:

 

[nikki]

I'd try a BR8ES (a hotter plug) - they are about $1.50 at the local auto store. I always ran a BR8ES in my 125's as did most of my friends.

 

[Rodp]

A Hot Burn?

What is a hot burn? When riding my bike on a trail band in sometimes and then not. I always like to get it a couple of good cracks open. Then it bogs out and stalls? Gone through 4 plugs so far and not much riding. I am using a B9EG that Yamaha recommends right now. May try an ES because they say their less fickle. But the bike is brand new...I don't understand it.

Rod

 

[topher04r1]

rod,

it sounds like you may have a jetting problem ... and even if the bike is new it doesn't mean the jetting is "right" ....also unless your doing some decent laps or hard core track time your spark plug heat range seems less than ideal..... try

reading this

:cool:

 

[Studboy]

You might try going down 1-2 sizes on your pilot jet. Stick with the 32:1 oil/fuel mixture.

BTW... IMO the Yamalube 2R is a superior 2T oil when compared to the Bel-Ray.

 

[89kdx200rdr]

the b9es plug will be fine for riding woods. stick with the yamalube at 32:1 or 40:1. how does it run on a new plug? your jetting is probably just in need of a little adjustment. i wouldnt go to a hotter plug to clean up a jetting problem. i think what the guy means by hot burn is usually when you are jetting your bike you do whats called a wide open throttle plug chop or thats what i call it. the chopping isnt anything to do with the throttle tho its the kill button, keep the throttle open and pull in the clutch as u kill it.

 

[moabdaze]

the b9es plug will be fine for riding woods. stick with the yamalube at 32:1 or 40:1. how does it run on a new plug? your jetting is probably just in need of a little adjustment. i wouldnt go to a hotter plug to clean up a jetting problem. i think what the guy means by hot burn is usually when you are jetting your bike you do whats called a wide open throttle plug chop or thats what i call it. the chopping isnt anything to do with the throttle tho its the kill button, keep the throttle open and pull in the clutch as u kill it.

That was what I meant. Hot burn and a plug chop are one in the same. Refer to the post several back w/ the jetting tips. That gives you detailed info on how to perfrorm this test properly. Good luck.

 

[Jeffack1]

I have a 2000 YZ125 and have had the same problem that you are describing. I raised the clip one notch, checked the fuel floats and they were not parallel so I lined them up, changed to a BR8EG and backed out the air screw from 1.5 turns to 2 turns. The bike is stock and these changes were made from the stock settings.

Also, when I first got the bike I was using BelRay and switched to Yamalube when I was fouling plugs left and right. I am still using Yamalube at 32:1.

I will still foul a plug on occassion especially when somebody rides the bike and does not stay in the rpm's but other than that, I would say that I have it worked out.

Good luck!

 

[soldsoul4foos]

04 yz125 compression

Hi,

My buddy has a 04 yz 125 that is fouling plugs like a mofo. gas and spark seem to be fine. he wants to check the compression, but we can't seem to find out what a recommended or good compression reading should be. anyone got a number? thanks.

[email protected]

 

[#1YZ125RACER]

i also have a 2000 yz 125 i run a 1 step hotter plug and spectro sx at 40:1 never any problems

 

[DrF324]

Sounds to me like the clip on the needle is set too rich u mite want to lean it up a little and try that to lean it u need to move the clip down a notch or two but if u have never had the needle out then u should have someone that has help u best of luck. :cool: