KDX220 not running right

[big gear head]

I've had this '98 KDX220 for a few weeks, but I've only had it out 2 times. The first time it was not running right, but still had pretty good power. The second time it ran ok for a little while, then it left me stuck on the side of a hill 2 times. It would run all right just off idle, but when I opend the throttle it would bog like the choke was on. I did a leak test on it and it was leaking real bad. Over the past 2 weeks I've been working on it. I rebuilt the carb and did a complete top end rebuild with a new Wiseco piston kit. I put a new Clarke tank on it while I had it apart. I tried to install the FMF fatty pipe that I got with it, but it wouldn't fit. When I got everything back together yesterday and warmed it up it still ran like the choke is on. It also won't idle on it's own. I have the idle screw all the way in and it still won't run on it's own. I did another leak test on it and it's sealed up tight now. Any ideas what might be wrong? It has the stock pipe and silencer on it.

[mlyle11]

Did you check the reeds closely when you did the top end? There is a lot of info out there on inspecting them for chipped edges. Also, I'm not sure about this on your year bike but does the bike have a power valve? Could be somethin there if it is not opening up as RPM's go up. As far as the idle, it seems fuel/air related. Are you sure the carb went back together OK? Needle and seat wore out? G'luck! and please post the fix once ya get it!

[big gear head]

The reeds looked like they were almost new. No space under them. They set flat against the block. I think they have been replaced receintly. The carb went together well. I replaced some parts, but the needle looked very good. I have a new one coming, but I doubt that I needs it. I set the float level with the sight tube, so I'm pretty sure that it's not the problem. I checked the valves several times as I was putting it back together to be sure that they were in time and free. I didn't check them after the engine was running to see if they were opening, but I don't know of any reason that they wouldn't. I might try to get the cover off of the shaft to see if they are opening.

I'm going to check the manual to see how to clean the spark arrestor. It might be cloged. I was wondering if it might be something in the ignition that's causing the problem.

[mlyle11]

What plug are you running? You could try a hotter plug, though this is more of a tuner fix, not necisarily for the bog. It's mostly a band aid for bad carb tuning ? I haven't heard of a lot of good ways to celan a plugged silencer... tear apart and repack maybe.

How about the changing the clip location on the jet needle? Maybe move it down a notch?

Also assuming a sparkly clean air filter and new plug as well right? Sorry, had to ask, ya never know!

Below is post I've used before. It really could be in the carb set up:

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.

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[big gear head]

The plug is the same one that was in it when I bought the bike. I cleaned it with carb cleaner and checked the gap. It seems to be all right, but I bought 2 new plugs and I'll try one of them. The filter is clean. I even took the filter out and it didn't help any. I already lowered the clip on the needle and that didn't help. When my new jets get here I will see if that makes any difference. I'm also going to check the ignition timing to see if it is off.

Thanks for the replies. If you have any more ideas please let me know.

[OLHILLBILLY]

If it's the stock silencer, to clean carbon out of it, just take the bolt out of the bottom, start the bike, and rap on the silencer with a mallet. The carbon build up is supposed to break loose and either fall out the bolt hole or blow out the end of the silencer.

Sounds crude I know, but that's what the book says to do.

[big gear head]

OK, I took the plug out and beat on the silencer while the bike was running. When I took the plug out there was a lot of oil that ran out all over the brake caliper and wheel. If any carbon came out it was very little. I also checked the spark plug again and it was a BR9ES, so I put in one of the new BR8ES plugs that I bought. It's back to running like it did when I bought it. If I take it easy in 1st gear it's all right, but if I open the throttle all the way it doesn't pick up much. If I put it in 2nd and open the throttle it will bog and then it will pick up and pull hard. When I got done I noticed that there was oil on the swing arm again where it's blowing out around the seal between the pipe and silencer. This was in 5 minutes or less.

I took the cover off of the mag and there was water in it. Not a lot, but some. I'm going to pull the flywheel and check the timing marks and clean out all of the water when I get time. I'm also going to take the carb back off and figure out why the idle screw isn't doing anything. The air screw is not doing much either. If I turn the air screw all the way in the bike will stall, but that's about all it does.

[dirtrider 11]

I had the same problem with the my throttle stop screw not working turns out the screw dug a hole in my slide not letting it push the slide up

[big gear head]

How did you fix that? My screw is plastic. I'll check the slide and see if it's worn.

[SS109]

'98 220's came with plastic throttle stop screws?

[big gear head]

I don't know if it came with it, but that's what's in it now. It's a black plastic screw with a spring on it.

[dirtrider 11]

I think your talking about the plastic nob that goes over the screw,if it didn't dig a hole in your slide and the screw is plastic than maybe it's to short from wear

[big gear head]

No, the whole screw is plastic. I had it out when I had the carb apart. I'll take the carb back off tomorrow and check the slide. I also need to take a closer look at this screw. It might be out of some other carb and it might not be long enough for this one.

Edited May 31, 2011 by big gear head

[big gear head]

I pulled the fly wheel off and there wasn't any rust on it. The timing seems to be set right. I might try removing the silencer and see if it runs any better. I'm about to run out of ideas on this. I'm going to look into the carb again, but it's going to be a few days before I get a chance to do that. I still haven't got my new jets. I ordered them over a week ago.

[big gear head]

I've had a few others tell me that they also have a plastic idle screw, so I guess it is original. I took the carb back off and disassembled it. Everything looks good inside. All of the ports and restrictions are open. The idle screw is working, but even when it is screwed in all the way the bike will not idle.

Edited June 2, 2011 by big gear head

[big gear head]

What is the air screw suppose to look like on the end? Mine is flat. I expected it to look like a needle on the end.

[asg5265]

well first let me answer this, the idle screw is plastic, that is stock on these carbs. and also lets look through a couple things first, is your stator working properly? Check the headlight to see if it works, if not then check your wires for corrosion and rust, on every circuit. IDK to be honest with you how well those bikes ran with the stock exhaust, I cant imagine poorly though. the next thing to check is the spark...pull it out, place it on the engine somewhere where you can see it spark and kick it, if the spark is not brilliant blue, you A) have a bad plug or ? have a bad connection/bad part. now time to check your jetting, have you changed your jets to the appropriate size for your area? does your bike even rev when in neutral? sounds like it just runs like crap no matter what. I would consider checking your 1) spark 2) jetting 3) fuel. do you have new fuel and good premix? consider these things before coming back here. these should pinpoint a problem, come back with your results on this test.

[asg5265]

you may need to consider a carb rebuild kit...

[big gear head]

The lights do work, and they are bright. I put in a new spark plug a few days ago and it didn't help much, if any at all. I haven't checked the spark. I'm still waiting for may new jets. They are suppose to be shipped tomorrow, so it's going to be next week before I get them. The fuel is about 3 weeks old and I used Kawasaki oil mixed 32:1. The tank is also a new Clarke 3.6 gallon and I cleaned it out well before installing it. I also cleaned the filters. I'll take the silencer off when I get everything back together and see if that makes any difference. I'm waiting on a new gasket for the fly wheel cover. It might be here tomorrow.

[big gear head]

I think I'm getting somewhere. I think the jet block gasket has been the problem. I replaced it and it's running better. The idle screw is working somewhat, and the air screw is also working a little. The bike picks up RPMs a little better and smoother now. I think it still needs some tuning.