KDX220 Questions: Slide Valves and Air Temperature Effects

Discussion specific to the 1995 - 2006 KDX200 (H Series) and 1995 - 2005 KDX220R (A Series) models sold in the USA
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billie_morini
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KDX220 Questions: Slide Valves and Air Temperature Effects

Post by billie_morini »

I'm writing with questions about valve slides and air temperatures for my 1999 KDX 220. One question involves carburetor slide valve replacement. The other question relates to the effect of temperature variation on carburetor jetting. Forum members thoughts will be welcomed.

The majority of my riding is slow speed with low to moderate throttle. Speed ranges are typically 12 to 35 mph (19 to 55 km/h). Within this range, I see a lot of 17 to 22 mph (27 to 35 km/h) with low to moderate RPM. Elevations regularly range from sea level to 4000 ft (1220 m) msl in a single ride.

I've been reading on the KDXRider forum about replacing the slide valve in KDX200 PKW35 carburetor with a leaner (#7) slide valve. Do you know of anything similar for KDX220? I'm also curious if you know how much air temperature variation effects / not effects jetting.

My KDX220 PKW33 carb is jetted relatively lean, but the engine is still running too rich.
  • Pilot jet is 38
  • Main jet is 140
  • Needle clip is P2
  • Float height is 18mm
  • Additionally, air box top is removed, Reeds are new Boysen dual stage, and exhaust is FMF "057" Woods with OEM spark arrestor
  • Pre-mix is 100:1 made with 91 octane + Amsoil synthetic Saber 2-stroke oil. (91 octane is highest octane available at pump in CA and usually has 10% ethanol in it. One of my close buddies has run AmSoil Sabre oil mixed 128:1 in a beastly, single cylinder 500cc two-stroke quad for years.)


Step-wise decrease in main jet to 140 resulted in fuel consumption increase from about 15 to 16 mpg (6 to 7 kmL) to 20 to 21 mpg (8.5 to 9 kmL) and was moving toward leaner engine operation until recently. I wouldn't mind improvement in mpg.

More importantly, spark plugs indicate the engine was running richer than any of the 4 previous rides. Two rides had large main jets than reported above. Two rides had the 140 main jet. The average air temperature here is consistently 68F (20C). Recently, air temperature was lower than average by 18F to 19F (10C to 11C). Therefore, temps were about 49F to 50F [9C to 10C]). It was damp, too. This is the day I got rained on twice while off road in mountains. The engine ran very rich and much richer than the previous 4 rides in which mpg and rich-lean ratio were incrementally improving. What are your experiences with KDX’s in temperatures that are about 20F (10C) lower than your average air temperature?

I do not know whether potential jet block gasket leak, lower air temps, or worn slide valve are causing this engine to run so rich. However, I'll have a new jet block gasket by Saturday for installation into my KDX220 Keihin PKW33.
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by SS109 »

billie_morini wrote: 11:41 pm Mar 30 2022 I've been reading on the KDXRider forum about replacing the slide valve in KDX200 PKW35 carburetor with a leaner (#7) slide valve. Do you know of anything similar for KDX220?
You can do the same to any PWK series carb. You can even do the mod yourself instead of picking up a new #7 slide. There are how-to articles and vids out there covering this simple mod. Whether you need it or not is a totally different question. I would make sure your carb and engine are in good working order before making this mod.
billie_morini wrote: 11:41 pm Mar 30 2022 Step-wise decrease in main jet to 140 resulted in fuel consumption increase from about 15 to 16 mpg (6 to 7 kmL) to 20 to 21 mpg (8.5 to 9 kmL) and was moving toward leaner engine operation until recently. I wouldn't mind improvement in mpg.
I'm confused, fuel consumption increased meaning it got worse, not better? I'm assuming you meant decreased.
billie_morini wrote: 11:41 pm Mar 30 2022 More importantly, spark plugs indicate the engine was running richer than any of the 4 previous rides. Two rides had large main jets than reported above. Two rides had the 140 main jet. The average air temperature here is consistently 68F (20C). Recently, air temperature was lower than average by 18F to 19F (10C to 11C). Therefore, temps were about 49F to 50F [9C to 10C]). It was damp, too. This is the day I got rained on twice while off road in mountains. The engine ran very rich and much richer than the previous 4 rides in which mpg and rich-lean ratio were incrementally improving. What are your experiences with KDX’s in temperatures that are about 20F (10C) lower than your average air temperature?
Temp, humidity, and elevation all play a huge part on your jetting requirements.

Colder temps mean denser air, warmer less dense. So...
Colder = more oxygen = increased fuel requirement = larger jets
Warmer = less oxygen = reduced fuel requirement = smaller jets

Humidity displaces air needed for the engine to run...
High humidity = less oxygen = reduced fuel requirement = smaller jets
Low humidity = more oxygen = increased fuel requirement = larger jets

Elevation is all about the oxygen available. Higher the elevation the less oxygen you have...
Lower elevation = more oxygen = increased fuel requirement = larger jets
Higher elevation = less oxygen = reduced fuel requirement = smaller jets

Really not a fan of the Saber oil, or 100/1 ratios, but to each their own. Not heard of many that like the "Woods" pipe on the 220 either. I run the "Desert" version.

Something really doesn't sound right with your jetting. You are extremely lean. Wouldn't be surprised if the jet block gasket is the problem. Curious, what needle are you running? Are you using genuine Keihin jets? Are you following the proper procedure for setting the float height correctly? Your jetting should probably be at least a step or two bigger on the main, even with that 100/1 ratio, compared to mine with you at sea level...

RB modified PWK35 bored to 36mm
2000ft asl
148m
38pj
CEK needle - 3rd clip
AS at 1.25-1.75 turns
18mm float height
Boyesen RAD valve w/carbon fiber reeds
RB head mod (listed because it does make a difference jetting wise)
no air box lid
FMF Desert pipe
FMF turbine core silencer
40/1 ratio
91 octane 10% ethanol
50-70 degrees F
10-30% humidity

To give an example of how much temp, elevation, and humidity can affect your jetting, I did a recent ride in San Manuel, AZ that illustrates it perfectly. It was on average 2000ft above my normal, temps were up to the mid 70's, humidity was about 15%. My bike was running decent at first but as the elevation and temps got to their highest my bike was running really rich as I was still on my winter jetting that I listed above. It was blubbery, stalling really easy, and even flaming out. It was so bad that I had to adjust my idle up to help with the overly rich condition. You can hear it in my vid (https://youtu.be/rh-wltHXPrQ) of the ride where at that time the temps were at their highest and we were about 4600ft asl. So, increased temps plus more elevation = pig rich. I should have dropped one size on the main and the bike would have been running great for that ride. Now, for my local riding I'll be raising the clip on the needle to the #2 position for this week and I'll drop the main one size once the temps hit the mid 90's.

Oh, another thing when riding such extreme elevation and/or temp changes during a ride is that you'll probably need to adjust your air screw leaner as temps and elevation go up and richer as they go down during the ride. The air screw is not one of those things that you just set and forget during a ride and sometimes could need to be adjusted several times.
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by John_S »

I can’t be much help with the jetting and elevations. I’m always at sea level riding in Florida. Before you change out your jet block gasket you should do the leak test just so you know whether or not it has been part of the problem. I would still change it anyway based on the age and the fact that you already have it on the way. And then test it again after you change it to make sure it’s all good. It’s a quick test to check it. Type in PWK jet block on YouTube and there’s a great video showing how to use compressed air to check it.
Someone posted a response from Sudco recently that stated the stock KDX 35 uses the same slide as the 35 air striker. If you look at the slide chart on Jets r us the PWK 33 also uses the same slide part numbers as the 35 air striker. I would think the #7 slide is going to affect the 200 and 220 similarly with 33, 35, or 35 air striker.
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by John_S »

My 220 has the air striker and although I’m happy with the way it runs, I don’t think the 4.5 slide that comes with it is optimal. The only complaint that I have is when the engine is fully warmed up and I start it I have to blip the throttle for about 5 seconds for it to stay idling, then it’s fine. My other bike has a 38 Air striker with a #7 slide and cold or warm it purrs on idle as soon as you kick it over. I emailed RB Designs yesterday morning and asked him about the his slide mod. He said let me know what you want it cut to and send it in with $30 cash, check or money order. I’m going to try it out.

Considering your slide is 20 years old I don’t know that I would have him modify it but his site still says he’s doing the 220 head mod. I have that done to my bike and besides the increased compression I really do think that it made the bike easier to jet and seems to stay a lot more consistent with humidity changes.
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by MoonStomper »

I posted that nugget about the slide being an Airstriker type. This I learned from emailing SUDCO. Besides swapping in a fresh jet block seal, definitely call SUDCO and let them recommend a slide. Even if you already have the correct size, slides wear out and a fresh one makes a huge difference in throttle response. Personally, I’d call Jeff Fredette about the needle and jets. He’s got that dialed.
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by billie_morini »

Appreciative of input received to date. Work day started at 0800 and ran to 2400. So, will be brief herein because of this. More later following thorough review of provided info.

@SS109: I'll try to 'xplain main jet & mpg. MPG increased when main jet decreased. Originally, 145 main jet provided 15 mpg. 142 main jet provided 18 mpg. 140 main jet provided 21 mpg.

G'night all
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by SS109 »

Cool. I thought that was what you meant but wasn't 100% sure.
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by billie_morini »

No news to report, yet. Limited free time went to: 1) Saturday dirt ride in outback wilderness on my DRZ, and 2) re-jetting my nephew's DRZ. Still appreciative for all KDX forum replies
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by billie_morini »

SS109,
Yes, only genuine Keihin jets

Needle: R1173L, clip at P2

Floats: set correctly

Woods pipe on 220: bought it this way. Have heard about a few like this. May change it, but not rushing toward this

Jets are lean / Jets should be larger: Agree. This is why I came looking for model specific quirks
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by billie_morini »

Moonstomer,
Yes, recognize you shared specific info & experience w/ Sudco & slide valves. You even provided Sudco contact info. I wrote to Chad, but h has not yet replied. I will call him soon. Just didn't have tine last week
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by kdxdazz »

I ride at similar elevations to you but my temps are much higher, about 33c but I have always had issues with running rich, here is how I solved it, first thing I would do.is put the airbox and snorkle back on, you will be surprised how much leaner it runs like that, step 2 is modify the slide, lots of tutorials online, grind to a number 6 and test, if still to rich then use a 1174 needle, if still too rich grind slide to number 7
That airbox and snorkle is crucial, you are not racing Motorcross, when I bought mine the airbox was chopped and snorkle missing, I welded up the airbox lid and fitted a snorkel from a Kawasaki boss, it's about 10 percent bigger than stock, as soon as I did this the idle increased and I was riding up hills.a.gear higher due to the extra torque
1999 KDX220SR (KDX220-B5)
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by kdxdazz »

Forgot to mention don't use 100:1, that will change the fuel air ratio to be richer as you now have less oil and more gasoline , 50 to 1 is normal, 32:1 if running flat out on a Motorcross track
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by billie_morini »

Quick update: replaced jet block gasket. Photo shows new one on left and flattened, worn out original on right. Re-installed number 42 pilot jet and number 145 main jet. Kept float at 18mm and needle clip in P2. Short street ride seemed positive. Will attempt to sneak away from work for proper off-road test
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

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All week I've wanted to ride off-road for proper test. But, all week work has sucked up long work days. But, it was possible to connect with Chad @ Sudco. He is sending me #5 (OEM) slide valve. This will help me re-establish baseline conditions. After some trials with this, will see if a #7 slide valve seems useful.
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by MoonStomper »

Regarding the #7 slide, I don’t recall it being recommended on the 220, but Chad really knows his stuff and seemed very familiar with KDX quirks.

The 220 carb has a narrower intake which changes things. Also, since you are running the woods pipe that is different than most folk’s 220 bikes. But then, I wanted a woods pipe on my 200, and Fredette was like “no you don’t”… the desert pipe worked out great with all the other mods we did (Radvalve/lid removal/porting/jets/needle/#7 slide/gearing). I’ve heard several folks say a new slide really helps clean them up.
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Let the good times ROLL!!!!!!!!!!!!!!!!
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by billie_morini »

Sudco sent an OEM size slide for my KDX220. Sudco employee, Chad, taught me a little bit about slide valves. I wanted OEM because I'm trying to get to baseline. There has not been time to install it. Work continues to interfere with life.

When work slows own, I'll start a delayed KDX project. I've got all parts and materials to lower the suspension. Suspension components will be internally lowered by 2 inches (50 mm). I did this with my DRZ400 with fantastic results. One thing to like about lowering the suspension this way is it is easy to restore components to pre-mod conditions.
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by billie_morini »

Now we're getting close! The biggest problem was resolved months ago with forum member assistance. The biggest problem was caused by leaking jet block gasket (o-ring). The majority of my riding is low to slow speed. County roads are predominantly used to access trailheads from home. Most of my riding is in technical terrain and, very trials-like quite often. On the forest fire roads, I rarely top 18 mph (because I'm not out to break records or bones + the views are astounding). Therefore, I'm most interested in carb jetting for just above idle (chug) to 6,000 RPM. I spend a lot of riding time at no more than 4,000 RPM. The spark plug in the photo was installed new and reflects about 60 miles distance riding as described. With the jetting and reed valves that resulted in this spark plug color, low end throttle response is very crisp. Acceleration from about 3,000 to 6,000 PRM is as smooth as an electric motor (it's eerie).
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by SS109 »

Looks good. Glad to hear your getting it sorted and it runs great.
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by Mechdziner714 »

When were your crank seals last replaced? If they haven't that's likely one of your issues.
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Re: KDX220 Questions: Slide Valves and Air Temperature Effects

Post by billie_morini »

Mechdziner, thanks for the good idea. The answer is, "I don't know." Bought the motorcycle used and am slowly working through it. The seller claimed the crank was relatively new, but I haven't done anything to verify this. Like SS109 said above, "Looks good." So, I'm going to run it for 150 to 200 miles or so and see what happens. This is only 3 or 4 rides for me. If employment didn't suck the life out of me and leave little time for fun & relaxation, then I'd dig deeper and also do pressure tests. Ali in all, this isn't so pressing because the engine appears to be running & pulling superbly.
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