ahhhh jetting

[2stroker144]

i know i must be getting anoying with all my questions lately, but i am running my kx100 at 40:1, it is doing fine, no spooge or anything, but it is smoking alot, do i need to rejet, or should i run at the recomended 32:1 premix, thanks again and again

 

[Patman]

Have you done a throttle chop test to see what the plug looks like?

 

[_JOE_]

Like Pat said, the only way to be SURE of the main jet is a plug chop. When does it smoke? Full throttle, under load, half throttle, idle?

 

[2stroker144]

alright

 

[2stroker144]

swear if this gets answerd, no more questions.dont be a quader...

 

[Patman]

Where in Texas?

How about sticking with your original post.

Being less of a spaz will help your cause Grasshopper.

 

[IndyMX]

the difference between 32:1 and 40:1 isn't really enough to affect whether or not it will smoke.

Most likely the smoking problem is that you have it jetted way too rich.

So, pick a ratio, 32:1 if that's what your book calls for, and jet accordingly.

 

[Jasle]

you'll be fine with 40:1 on a kx80 IF you use quality pre-mix...not cheap stuff. Also the cheap wal-mart stuff tends to make more smoke.

You do need to check your plug. My guess is the bike was jetted for someone that races, and with you putting around on it, it is rich. The throttle chop is what i'd do for someone that actually runs it at WOT but if your new your probably not riding it all out. Your probably rich on the pilot jet and never revving it out.

It is a 2 stroke so it is going to smoke...There could be another problem with the right side crank seal. Big time bummer if this is it because you have to split the case on those to do the seal. it installs from the inside on the right side.

 

[jackflack44]

Preston, just bring your bike over to my house this weekend. Plus, if you're worried about smoke, running 32:1 would be richer than 40:1, which means more smoke.

Patman, he's from Flower Mound, outside of DFW.

 

[jackflack44]

And what is a plug chop? How do you perform one? I will just go ride really aggressively then go check my plug for symptoms. Is it in my Clymer? Stupid friends need to learn to work on their own bikes :think: Thank you for everyone who's helping, I'm learning new stuff too :nod:

:ride:

 

[jackflack44]

Anyone?!

 

[_JOE_]

You need to look at the ring that forms at the BASE of the ceramic insulator down where it meets the body of the plug. You will need to cut the threads from the base of the plug or buy a special viewing tool to see it.

This is only effective for the main jet and should be done on a new plug. Warm up the bike then run it wide open through all the gears and when it tops out pull the clutch in and kill it. Take the plug out and chop it. There should be about an eighth inch wide ring at the base of the insulator.

 

[jackflack44]

can you do that on a stand?

 

[_JOE_]

Umm, no. You should do it on a slight upgrade so there is a consistent load on the engine.

 

[jackflack44]

There are 6 gears so I've no idea how or where to do that...

 

[Patman]

Well then I guess just don't do it because that's a heck of a lot easier than trying to find a place.

 

[whenfoxforks-ruled]

The premix more than likely has nothing to do with the smoke. A friend had his kx done up at Forward Motion, Eric told him to run 20:1 and jet it accordingly. Smoke that! You need compression and the bottom end tested to see if its sealed. That is a leak down test. Verify that the timing is correct. 1999, replace the float valve and seat if applicable. Fresh premium fuel and jet the bike. To your knowledge has any work been done to the motor, like ported and polished, mods to the head? When is the last time the reeds and packing have been replaced? Do you have a shop manual? 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.

 

[2stroker144]

jackflack is stupid thankyou all for helping me pops and i just got done jetting, she runs great and smokes alot less, thanks everyone