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.