one more KX65 piston picture: lean condition?

I can see the spot now.

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.

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

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