KDX220 questions (throttle resp/power band)

[sierraKDX]

Hi All,

Picked up a 2000 KDX220 last week (very clean, $2200 California).

Have some q's about it:

1) Right off throttle it seems to stumble a bit. Hard to explain, a stutter, stumble, miss, sputter. If you keep the throttle there, it is not very fun to ride, like on really tight trails where you are navigating slowly. Is this normal? I have ridden limited other 2 strokes, and have noticed some do have a flat or stutter throttle range, but not quite the same as this. It feels like a plugged jet, is there a separate low speed jet? Otherwise, just a bit more gas and WHOOSH! Which leads to the next question.

2) Does this thing really have a power band? My kid's KX85, stock except FMF TCII has a very pronounced one very high up. The KDX220 goes very strong right off the bat, and seems pretty consistent all the way up to some seemingly high revs. I have not yet really "red-lined the p&ss" out of it so I am not sure if there is more to go. Is the power band lower and flatter on this bike?

Generally the bike is a kick. It rides more like a 4 stroke but feels lighter and and more responsive. It is super quiet as well, most people think it is a 4 stroke based on the sound (stock).

I love it. Thanks in advance!

Scott

 

[Green Hornet]

Jetting!!!

 

[kdx220dave]

I have a 220 also.
You need to loose the air box lid and put in a uni or similar air filter. I am using a smaller pilot and advanced the timing slightly. Mine barks right off the bottom. Oh ya I also have a FMF Gnarly pipe and FMF turbine core silencer. I can get you the exact jet numbers if you need them.
Happy Trails Dave

 

[sierraKDX]

So the stutter right off idle is normal for a stock 220? Thx, Scott

 

[apb]

I'm far from an expert on this stuff, but this jetting guide does a good job of walking you through getting the jetting right -- sounds like your problem might be in the slow circuit -- the bogging will probably be cured by getting the right pilot jet, air screw, and needle clip position. Keep in mind, as the weather gets colder, you'll need to richen the jetting to prevent a lean condition. Where abouts in the sierra foothills are you, by the way? I grew up (and still do my riding) in the foothills of Butte county above Chico.
Before you start jetting, though, you should first clean the carb and air cleaner out well, and put a new plug in. Good luck.



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.

 

[Green Hornet]

"stutter right off idle is normal" NO

 

[adam728]

Your stutter could be something as simple as the airscrew needing adjustment. That's where I would start. There are lots of posts on how to do that.

And the 220 doesn't have any sort of hit in the powerband when stock. It's electric smooth, but does not rev all that high.

 

[sierraKDX]

Ok sounds like I am on my way THANKS GUYS!!!!

Scott

 

[Yamadad]

Go to the FMF website and check their stock jetting specs (if you don't have a manual). Then pull your carb open and check what you have, then adjust from there. Always start from stock, that way you have a baseline. I too agree that your jetting sounds off.

 

[Kaw4me]

I installed the 6mm slide today.

Man , what a difference ! :cool:

I didn't realize how much the stutter " rich " was effecting the
bottom end as now with just a quick blip of the throttle she'll
pick the front end.

I only had time for a short ride but this is deffinitly a major step in
the right dirrection. :nod: :nod: