KX500 PWK39 Jetting Discussion - My Experience

Dirt Bike Technical discussion. This is for a little more in depth discussions :-)
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Pile-O-K5
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Joined: Wed Jun 03, 2020 1:52 am

KX500 PWK39 Jetting Discussion - My Experience

Post by Pile-O-K5 » Sat Aug 29, 2020 9:18 pm

I want to keep this short. I was chasing a rich condition from idle to 1/4 to 1/2 throttle and my bike would not idle without the idle adjustment all the way in. Changing Jets did not seem to make any difference and for the most part I had the bike setup with a 55 pilot. I used a whole tank more or less in a 30 km/19 mile ride and was not a hard ride by any means. Mostly ditch banging. For a test I slammed a 50 pilot in and a 60 pilot. Both would die with the pilot adjustment screw turned in all the way and would run with the screw removed from the carb without an observed change to the idle. Something was not right. Spark plug was wet with fuel and carbon fouled.

Thanks to this thread:
viewtopic.php?f=108&t=1472

I was able to solve the issue. The jet block or mid block o-ring was bad.

My final jetting is now as follows:

+/-2200'
27 Celsius/81 Fahrenheit (today)
19% humidity
Slide #7
Main: 168
Needle N82M #2 From Top
Pilot: 42 - 1-3/8 turn out

The motor setup is OEM Cyl, Head, Crank, PWK39, 10mm Carb Spacer, VForce 3 Reeds, FMF Gnarly Pipe, Powercore Silencer, BR8EIX plug, and timing set to OEM 17 deg. BTDC @ 6000 RPM, 15/47 gearing.

With this jetting, the idle is good there is not any surging and the idle settles in immediately, no hanging. The bike has great power and pulls cleanly from the basement to the roof. The bike did not get over 172 Fahrenheit, per the Trail Tech TTO coolant gauge. Hit 8800 RPM peak on the TTO gauge in lower gear most likely and a long 5th gear pull hit 8000 rpm.

I'm happy and the bike seems happy too. :lol:

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Sandblaster
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Re: KX500 PWK39 Jetting Discussion - My Experience

Post by Sandblaster » Sat Aug 29, 2020 9:55 pm

On the top mount of your pipe there should be a stamped number.
It will end with either 55 or 38.
Which do you have?
If bikes are for kids I'll never grow up.

Pile-O-K5
Posts: 13
Joined: Wed Jun 03, 2020 1:52 am

Re: KX500 PWK39 Jetting Discussion - My Experience

Post by Pile-O-K5 » Sat Aug 29, 2020 10:10 pm

The only number that I could see stamped on the upper pipe mount was 1202-020055. The pipe was still mounted to the bike. Does the stamping indicate the woods versus desert pipe? Is the stamp you are reffering to in a different location?

Edit. I just realized. I'm an idiot. The number ends in 55.

Image

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Sandblaster
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Re: KX500 PWK39 Jetting Discussion - My Experience

Post by Sandblaster » Sun Aug 30, 2020 4:42 am

You should be making about 56 RWHP with that set up.
Very respectable numbers.
If bikes are for kids I'll never grow up.

Pile-O-K5
Posts: 13
Joined: Wed Jun 03, 2020 1:52 am

Re: KX500 PWK39 Jetting Discussion - My Experience

Post by Pile-O-K5 » Sun Aug 30, 2020 6:21 am

I forgot to mention that before I replaced the mid carb o-ring that I put both a 45 and 48 pilot jet in and it exhibited the same conditions as the 50-60 test. I was worried when I was done and it wanted the 42. There is only a 40 and 38 left to drop to. The pilot screw responds as it should though and the idle adjustment screw is not all the way in.

I won't argue with your assessment of power. I'll never be able to put it on a dyno to tell the actual numbers, but I am very happy with the power it now has. I am also relieved that I was able to get it sorted out. It was giving me issues since I rebuilt it 2 years ago, progressively getting worse. I didn't even realize that there would be a oring in the carb, the OEM parts fiche for the bike does not show the mid carb o-ring.

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Sandblaster
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Re: KX500 PWK39 Jetting Discussion - My Experience

Post by Sandblaster » Mon Aug 31, 2020 3:33 am

Your right.. It's not shown anywhere except carb sites.. Sudco and keihin.
Unless you know, then you can find them on ebay,,
If bikes are for kids I'll never grow up.

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