Kdx220 Jetting Problem

[jaguar]

>runs better with a load OR during acceleration than it does at constant throttle.

that's too rich

 

[KylePeterson]

>runs better with a load OR during acceleration than it does at constant throttle.

that's too rich

agreed, it's fouled two br8eix iridium plugs (or three, i don't remember). i switched to the br8es (non iridium) plugs, and got two full days of single track out of it without issue. i did a couple of plug chops with new plugs after the ride, while the bike was still HOT to get a decent read of the plug.

the attached picture is a 3rd or 4th gear WOT chop, running Lucas oil 32:1, 38/136, middle on the needle, and 2 1/4 turns out on the mixture screw. it pops a little on deceleration (down hills) and pulls strong from the basement to the sky. but, that nasty off-idle sputter is still there at steady throttle going down the road.

the colors of the plug are misleading in the picture, so i'll clarify what they really are:
plug threads and face = biscuit tan / brown to oily spooge
plug insulator = gray to black deeper in
bent electrode = gray to black
electrode = black




****
last week i rode a rmx250, and expected a similar sputtering when held at constant speed on the road (connecting trails). it was smooth as silk running at 35-50mph in whatever the top gear is. really made me want to make my kdx run better, as that bike is much more managable at cruising speeds. i know the kdx is a woods bike, and a love it in the woods, but if this isn't possible, i may need to starting looking for an old rmx250 to pick up and resurrect. the wide ratio transmission was really nice, and it pulls so mildly from the bottom, with an even more linear power curve than the kdx.... i liked it. a lot.

 

[KylePeterson]

UPDATE

after much running around, much jetting changes, and much much much searching for info i finally shatter-shot the problems into submission.

problems:
1 reeds looked fine, but were not tight
2 timing was retarded 5 degrees (estimate)
3 premix was poor quality oil (i learned i learned, forgive me!)
4 trash in the intake port
5 arrestor was broken inside, resulting in 1/2 the air flow of a good pipe

remedies:
1 new boyesen reeds for the Rad Valve, which has no markings on it, so it took some googling to figure out why my reed cage wasn't like all the other 200 /220's reed cages.
2 reset timing to 5 degrees advanced (most advanced STOCK marking)
3 changed to lucas semi synthetic premix oil, at 40:1
4 cleaned that out, after pulling the cylinder and finding it
5 changed to a ProCircuit stainless rev pipe arrestor

finalities:
bike has not fouled a NGK BR8ES plug yet. it starts easily, idles smoothly (i keep my idle a little low to be quieter during warm-up) and pulls very nicely from idle up to WOT. KIPS is functioning normally, opening as it should to bring on the rush of top end power.

this is the results on yesterday's street ride:

which is pretty good, but still not perfect. i'll pull a plug after some woods riding and see how it compares.


my only complaint now is the stuttering, or what i've seen described by others as "four stroking" the bike does while at constant throttle. if there is the slightest load (uphill, too tall a gear, slight acceleration) the bike will smooth out instead of putttaputtaputta. if this is a characteristic of the kdx, i'll live with it. maybe i should go up a tooth on the front sprocket to give it a small load and smooth things out ?

yesterday I spooned on some old Avon Distanzias, and found they are a fantastically smooth running street tire. there is a gymkhana this saturday in Falkville, AL, and I plan to take the drz400 and the kdx220 to play at the event. i've only ridden the bike in shorts so far, so the lean angles have been very very mild. i'll break out my leathers for saturday, and get silly. ;-)

the test ride with the distanzias was short, smooth, and i only acclerated to around 65mph while on a major highway, you can see the RED section indicating higher speed, and the cooler blues/greens indicating slower, neighborhood-friendly slower speeds:

i'm really impressed with the manageable power of the kdx while in street trim. first gear is useless in street mode, but that's easily rectified, just change to second or third and start off smoothly ;-)



i've got to say, after all this mess, the kdx is still my favorite bike to pull out of the garage. it helps that it's street legal (tagged) and almost 100 lbs lighter than my drz.

now, it has me thinking i might pick up a worn out kdx or rmx and supermoto it with gs500 wheels.

end of rambling, the bike is good.

thank you dirtrider members, for sooo much :)

 

[Rich Rohrich]

my only complaint now is the stuttering, or what i've seen described by others as "four stroking" the bike does while at constant throttle. if there is the slightest load (uphill, too tall a gear, slight acceleration) the bike will smooth out instead of putttaputtaputta. if this is a characteristic of the kdx, i'll live with it. maybe i should go up a tooth on the front sprocket to give it a small load and smooth things out ?

Sounds like it's still too rich on the needle and possibly the pilot jet as well. Given that it's an older bike it's worthwhile to check for wear on the needle and the needle jet.

You can't hurt the engine from running too lean a pilot jet, and in almost all cases that will be true of the needle position as well as long as the needle jet has enough area to feed the main at WOT, but that's easy to verify. For the type of riding conditions most will encounter the worst that comes from being too lean on the pilot is a hesitation/bog. If you get way too lean on the needle it will be obvious from the performance most of the time. Worst case on the needle posiiton being too lean is possibly some spark knock in low speed, high load situations where the throttle is open past 1/2 and maybe a throttle run on coming down from high speeds.

No one ever broke an engine from running too lean on the pilot. Lean is good in the low speed portion of the fuel curve.

 

[KylePeterson]

Sounds like it's still too rich on the needle and possibly the pilot jet as well. Given that it's an older bike it's worthwhile to check for wear on the needle and the needle jet.

You can't hurt the engine from running too lean a pilot jet, and in almost all cases that will be true of the needle position as well as long as the needle jet has enough area to feed the main at WOT, but that's easy to verify. For the type of riding conditions most will encounter the worst that comes from being too lean on the pilot is a hesitation/bog. If you get way too lean on the needle it will be obvious from the performance most of the time. Worst case on the needle posiiton being too lean is possibly some spark knock in low speed, high load situations where the throttle is open past 1/2 and maybe a throttle run on coming down from high speeds.

No one ever broke an engine from running too lean on the pilot. Lean is good in the low speed portion of the fuel curve.

great points, thanks for helping out with the feel side of the jetting.

it ran fantastic yesterday in 95F heat, on a parking lot, all day (gymkhana) with street tires. several people went for joy rides on it, and ripped up/down the road at WOT in top gear. no issues besides the mentioned stuttering at constant throttle. no one complained about ridability, lack of power, or well, anything. grins were everywhere when they returned the bike.

given what you've said, I'm going to look for a replacement carb that is either new or very low hours, given that this model isn't fully rebuildable. i have a pwk35 (i think) in the basement, but want to try a much lower hour carb and see what happens.

right now i have about 15 hours of riding on a BR8ES, and it's still looking good. i'm going to continue to carry spare plugs, just in case, but hopefully this is soon to be a non-issue.

thanks again for your help.


here's the mix of "NO FUN" signs which the kdx typically breaks at any given moment:

i don't think i mentioned it yet, but i've also changed from weedeater oil (yuck!) to Lucas emi-synthetic, and enjoyed a much cleaner running engine. There is no smoke, a little bit of head pipe spooge, and none out the tail. I'm not kidding, at 40:1, once warmed up, there is NO smoke at all. it's only when the bike is warmed up, or at WOT runs that it will occasionally put out a signature two-stroke plume. even then, it's very minimal. the kips seems to be free of the normally gummy/sticky mess, and only be covered in a thin (3in1 like?) coating, which wipes off easily. the tail pipe is spotless.

until told otherwise, i'm going to stick with lucas semi-syn for a while. i'm completely NOT a brand loyalist, but so far, i don't know any better. :)

edit complete :)

 

[KylePeterson]

Last weekend I tried out a homemade airbox lid. I wanted to protect the filter from debris, since there is no lid on it at all right now. First, I drilled two 1 1/2" holes in it, to simulate the stock airbox lid's opening. The bike started without choke from a cool (75F) garage, whereas it would usually require choke. The idle was blubbery, and I couldn't effect the idle with the idle screw at all. Running was smoother, but power was down. The bike smoked with this configuration, meaning the jetting was definitely fatter.

Next I drilled an additional 1 1/2" hole in the airbox lid. This helped with idle slightly, and power was a little better. Still smoking, still noticably fat.

I pulled the cover off for a test ride, and the idle adjustment screw was usable again. It required choke to start (from cold) as it should. The power was better, I should say there was MORE, so much as it was more crisp to initial openings.

The two main things I wanted were:
some protection from debris
a big reduction in airbox noise

I accomplished both, but at the cost of proper jetting. I suppose I could lean out the jetting to match the airbox lid, but it's going to be over 100F this weekend, and I doubt I'll do any testing or riding, in that heat.