2002 KDX 220 Jetting Comparison

A reference for the PWK carbs...
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Willbilly
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2002 KDX 220 Jetting Comparison

Post by Willbilly »

Team,
I have a 2002 KDX 220 with FMF Gnarly Rev pipe and FMF Turbine Core 2 muffler, Boyson Power Reeds, recently replated cylinder from Power Seal USA matched with a new piston, all power valves recently cleaned, fresh gaskets in the stock PWK 33 carburetor, and all tuning done with clean air filter, fresh fuel, and fresh muffler packing. I ride between 0' and 1000' above sea level in southern VA. Currently the temperatures average 65 degrees with humidity ranging from 50% to 90%.

Using the jetting guide I have a 35 pilot, 140 main, stock needle at the 1st clip from the top, air screw turned out 2.5 turns and float bowl height of 16mm. I'm going to change the needle because I don't like the clip location and I think the 1/8" throttle to 1/4" throttle position could be more crisp. The temperature is getting hotter and more humid and its looking like i'll have to drop the pilot to 32.

My question is, do you yall think my pilot jet size, needle clip position, air screw position, and main jet size are odd?
Last edited by Willbilly on 01:41 pm May 18 2017, edited 2 times in total.
John_S
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Re: 2002 KDX 220 Jetting Comparison

Post by John_S »

Yes those jets are small especially if you have a 35 carb. Did you mean stock 33? A 35 pilot jet is as small as it gets for the PWK. I believe the cure will be setting the float height to 18 instead of 16mm. That should lean it out just enough that you can get back to having some adjustability with your pilot and needle clip. Blow air through the fuel inlet when your floats are at 16 now just to make sure the float valve is sealing. If it's not that would cause a rich condition needing small jets. Also make sure the reeds are still good.

If you have the 33 carb I would go with 18mm float height, 40 pilot, 1 1/2 out, stock needle 2nd or 3rd clip, and 145 main and go from there using the jetting guide. Unfortunately you have to start jetting from scratch again if you change float height but you're already tapped out on the pilot circuit at 35, 2 1/2 out, and stock needle in the top clip.

My brand new 35 AS was excessively rich at 16mm and would also piss out the overflow if the bike was on a triangle stand. I was still too rich with a 35 pilot. 18mm float height fixed it.
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Re: 2002 KDX 220 Jetting Comparison

Post by ohgood »

Saved for future reference
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Re: 2002 KDX 220 Jetting Comparison

Post by John_S »

I forgot about the jet block oring incase that wasn't one of the gaskets you mentioned replacing. Try this before any float height adjustments. I've never been able to move it like this guy did and fix it. It needed a new oring on the couple that I fixed.

Willbilly
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Re: 2002 KDX 220 Jetting Comparison

Post by Willbilly »

John_S wrote:Yes those jets are small especially if you have a 35 carb. Did you mean stock 33? A 35 pilot jet is as small as it gets for the PWK. I believe the cure will be setting the float height to 18 instead of 16mm. That should lean it out just enough that you can get back to having some adjustability with your pilot and needle clip. Blow air through the fuel inlet when your floats are at 16 now just to make sure the float valve is sealing. If it's not that would cause a rich condition needing small jets. Also make sure the reeds are still good.

If you have the 33 carb I would go with 18mm float height, 40 pilot, 1 1/2 out, stock needle 2nd or 3rd clip, and 145 main and go from there using the jetting guide. Unfortunately you have to start jetting from scratch again if you change float height but you're already tapped out on the pilot circuit at 35, 2 1/2 out, and stock needle in the top clip.

My brand new 35 AS was excessively rich at 16mm and would also piss out the overflow if the bike was on a triangle stand. I was still too rich with a 35 pilot. 18mm float height fixed it.
I meant the 33, thank you for clarifying that. I can find pilot jets down to a 30. If the float valve closes I don't understand how a float height will affect the richness, could you help me understand? My float is at the recommended height at the moment. I will check the reeds, it has been about four months since i've inspected them. The jet block O-ring and all gaskets were replaced in the last year and I have not used any carb cleaner in the carb since.
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Re: 2002 KDX 220 Jetting Comparison

Post by John_S »

Genuine Keihin pilots only go down to 35 according to jets r us. I tried aftermarket (ProX) pilot jets before and NEVER again. One size to the next and it was all over the place. I've read before that float height can be 16mm +/- 1-2mm and still be considered within spec. I first started reading about altering float heights studying YZ250X's and 17KTM300's. Guys were talking about having to lean out the whole mixture by raising the float height measurement to get them to run correctly. Changing my float height to 18mm really did make a difference. I have no idea how it all actually works so I just googled "float height affects rich and lean". There is way more information than I would want to read about regarding low pressures, high pressures, vacuum etc. Below is one of the simplest explanations I saw on a forum....

I just found this in spanky's thread:
THE FLOAT LEVEL IS THE FIRST STEP TO PROPERLY DIALING IN YOUR JETTING. It should be checked and/or set before you even think about swapping brass. By altering the volume of fuel in the float bowl you can vary your fuel pressure and affect your jetting. More fuel in the float bowl will create more fuel pressure and result in rich(er) running conditions and vice versa.
Willbilly
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2002 KDX 220 Jetting Comparison

Post by Willbilly »

So if I wanted less pressure by having less fuel in the float bowl wouldn't I want to set the float height to a less number than the recommended height rather than more?
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2002 KDX 220 Jetting Comparison

Post by John_S »

Willbilly wrote:So if I wanted less pressure by having less fuel in the float bowl wouldn't I want to set the float height to a less number than the recommended height rather than more?
This picture showing how you're supposed to hold the carb (45 degrees upside down) while measuring the float height so the tang is touching the float valve plunger but not pressing it in. In the first picture the measurement would be larger than 16mm from the peak of the float to the gasket surface, so less fuel in the bowl once back on the bike. The second picture would be 16mm, so more fuel once back on the bike.

https://goo.gl/images/G8LQ4j

https://goo.gl/images/b0khMg
Willbilly
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2002 KDX 220 Jetting Comparison

Post by Willbilly »

John_S wrote:
Willbilly wrote:So if I wanted less pressure by having less fuel in the float bowl wouldn't I want to set the float height to a less number than the recommended height rather than more?
This picture showing how you're supposed to hold the carb (45 degrees upside down) while measuring the float height so the tang is touching the float valve plunger but not pressing it in. In the first picture the measurement would be larger than 16mm from the peak of the float to the gasket surface, so less fuel in the bowl once back on the bike. The second picture would be 16mm, so more fuel once back on the bike.

https://goo.gl/images/G8LQ4j

https://goo.gl/images/b0khMg
My brain was backwards. I will do this soon and report back.
Willbilly
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2002 KDX 220 Jetting Comparison

Post by Willbilly »

Update:
I dropped the float bowl to 18 mm from 16 mm. No gain on performance. The carb at this point was 35 pilot, 140 main, 1st clip, 2.5 AS.

5/27/17: I broke a cardinal rule and changed the main to 138 AND dropped the needle to 3rd clip. There was no spooge but I had no top end.

5/28/17: changed the needle clip to 4th down. Same as the day before. I also fouled 2 plugs ??????

5/29/17: found out the reeds had a 1 mm gap on one side. Using RAD valves. I flipped the reeds. Now the bottom is extremely lean and the top runs great but I had an extreme amount of spooge. Turned the AS to 1.5. The spark plug is bone dry on the electrode and wet on the threads.

Changed pilot to 38, still weak in the bottom end, less spooge. ???

Next plans: go back to OEM reed valve with Boyson pro series reeds. Then if necessary increase pilot to 40.

Voo-fing-doo magic
Last edited by Willbilly on 01:20 pm May 31 2017, edited 1 time in total.
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Re: 2002 KDX 220 Jetting Comparison

Post by 6 Riders »

Don't know why you would flip the reeds, if they aren't seating correctly, they need to be replaced. You should be able to get reeds for the rad valve for the same price or less than pro series reeds.
Also sounds like (reads like) you're to lean on the bottom.

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Willbilly
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Re: 2002 KDX 220 Jetting Comparison

Post by Willbilly »

I changed the reed block back to OEM and installed new boysen pro reeds. Changed the pilot to 40. The bike performed better than ever but spooge was running half way down the exhaust pipe after half an hour of riding. Dropped the needle to 3rd clip. Will report back next ride.
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Re: 2002 KDX 220 Jetting Comparison

Post by John_S »

I'm glad to hear you're getting there. Sorry if I misguided you with the float level but I was in the same boat and that's what finally cured it. I had a heck of a time with a brand new 35 air striker with the float level and float valve intermittent sticking, combo problem.
Since clip changes are so quick on KDX's try the second clip also for a minute. It usually only takes one 3rd gear, LOW speed (high load) roll on the throttle to know if you went one clip too far.
Willbilly
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Re: 2002 KDX 220 Jetting Comparison

Post by Willbilly »

John_S wrote:I'm glad to hear you're getting there. Sorry if I misguided you with the float level but I was in the same boat and that's what finally cured it. I had a heck of a time with a brand new 35 air striker with the float level and float valve intermittent sticking, combo problem.
Since clip changes are so quick on KDX's try the second clip also for a minute. It usually only takes one 3rd gear, LOW speed (high load) roll on the throttle to know if you went one clip too far.
You didn't misguide me, I had to try it.

3rd clip runs fine still a lot of spooge. I will try 2nd next
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Re: 2002 KDX 220 Jetting Comparison

Post by HSV-Dirtrider »

Just picked up a 97 KDX220 so looking forward to seeing where you ended up. Does the 220 PWK33 use the same needles as the 200 PWK35 and is the CEL or DEL still recommended?
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