My Experience with Jetting, Mix Ratio, and a few questions!

[rbaker]

I bought my 00 yz 125 from a trusted friend who barely used the bike. He advised me to run 40:1 so i always use Yamalube 2-R however when i got it i would constantly foul out plugs and then i decided to tune it. I cleaned the airfilter out and made sure the exhaust was mostly clear and then went on with the adjusting.

I ride and live at an elevation of 90-100 feet so its basically sea level.

I had to go from the 3rd clip (stock) to the 2nd clip on the jet needle and 1 1/2 turns out (stock) on the mix screw and i have the idle set so it barely idles at a stop and dies after a few seconds.. I have the stock 350 main jet, stock 35 piolot jet, and an 80 starter jet.

I must say that the bike felt like a completly new bike after the tuning i made. It was absoutly amazing.. but then about an hour and a half of riding the plug fouled out.. so i cranked the mix screw out another 1/2 turn so its at 2 turns out now and threw a new plug in.. seems all good now because it ran great for the rest of the day. I am going to pull it out and check it tomorrow. If its nice and tan then i am going to be soooooo happy. But if not then its back to the drawing board for me.

Now i barely get any oil out the rear of the bike (but there still is a tad).. but to be honest an article i read which i found recently posted in another thread here, has really got me interested in going to full synthetic at 32:1 and setting my bike all back to stock specifications. What are your opinions guys?

Also.. what elevation are the stock recommended settings set for?

Thanks!
~rbaker

 

[ellandoh]

stock settings can usually be discounted as worthless :fft:
if you decide to do 32;1 then do it and see how the bike reacts

drool will probably come out after a rejet for a while from residual affects in the pipe and packing

if youre checking youre plug while riding like normal then ok but if your plug is a little rich and you are just tooling around to check the plug i would leave it unless you always ride easy

 

[rbaker]

Yeah, It was at the point where i was fouling a plug each ride / startup so it got insane! :coocoo:

But yeah tomorrow will be my day off so i can spend a few hours with the bike to perfect what i have started haha.

But with the massive increase in noticable power i felt im more then sure that i am on the right track now.

~Ross B

 

[ellandoh]

sounds like you got it covered but this article i found is still interesting :cool:



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.

 

[CaptainObvious]

rbaker,

First off, hello to a fellow NJ rider!

There are many things that affect jetting. At times it seems more of an art than science.

Are you running the bike at high RPM's? I've noticed with 125's that they like to live in the powerband. Operations at mid throttle tend to foul the plugs easy. On the last 125 I owned I could ride for months on the same plug, but as soon as I let my buddy ride the bike, he'd foul the plug. The jetting didn't change, but he was "taking it easy" on the throttle, where I rode the bike as if the throttle was an on off switch.

 

[sick 96 250]

Jetting can be a pain but it sounds like your on the right path of getting it situated. Like CO said, jetting can be effected by many things. Recently I jetted my bike and had everything dialed in. Went riding the following weekend and it was so hot and humid that my bike was running rich and I was fouling plugs. 2-strokes can be a pain sometimes but once set-up correctly their great. Good Luck :cool:

 

[rbaker]

Thanks for the replies guys I really do agree that i am indeed on the way to a really well tuned 00! I pulled the plug out today to just take a look at its color.. anyway it wasnt soaked like it used to always be and it was more of a medium brownish.. this makes me wonder if i am still running a tad rich. I may try a tank of 32:1 to lean it out a bit and see what happens from there.. any ideas?