one more KX65 piston picture: lean condition?

[MXTex]

This picture shows the bottom side of the piston out of my sons 2000 KX65. Notice the black spot. I believe this indicates a lean condition. Where should I fatten up the jetting? The way the motor sounded, I was thinking about raising the clip one position to clean it up a bit. But this pic has me thinking to richen things up. Maybe one size up on the main? Please advise. This is the original piston and I think the original jetting. Just bough the bike used but it looks pretty much untouched in terms of any tuning.

 

[Jaybird]

I can see the spot now.

 

[MXTex]

Thanks for the edit Jaybird. :)

 

[125 rider]

I have had spots like that on the underside of the pistons on just about every bike i've torn down. I think the size and color of the spot would be a better indication of jetting.

 

[MikeS]

Considering the photo on the other post, Lots of time is on that piston. One time run that overheated the bike could have made that spot and had nothing to do with jetting.

Check the rod (big end), Hone/deglaze that cylinder, recheck cylinder condition, put in a good replacement piston/pin/bearing, run good oil/fuel combo with a new clean air filter and plug. Run it/break it in ( do a couple cool down cycles. Then let junior run it around. Change the plug again and go do a WOT plug test and check the jetting. That way you can set your main on a fresh piston. You may find that you need leaner since the fuel is burning under the proper compression or you may need to go richer..... I would not use that worn piston as the final guide to a base line jetting.

good luck

 

[Shred]

MXTex, if you don't need that burnt piston, I'm looking for a KX65 piston for an experiment I'm doing. Please let me know. email: abj1835@yahoo.com

 

[MXTex]

Sorry Shred,
I tossed that piston out quite some time ago.

MXTex