How to read a piston.

[Tonykart5]

Look at this piston and try and figure out how it is running.

This is from a CR125 shifter kart after a race in Roebling Road Raceway , Ga, this past weekend.

Click the picture to enlarge

[fulltiltrider]

My guess would be, not as fast as it could be in a short distance due to the fact that you are probably running a tad rich to keep it together at high rpm for such a long time. But like I said in the other thread, properly jetting by plug is the way to go.

[Tonykart5]

Reading the plug obviously works for you. Thats good. This post is here to help with those who may want more out of there machine. I compete. And the competition is tough. Also its a go kart, so removing the plug and looking at the cylinder is much easier. Fine tuning your jetting using the piston as your guide is much more accurate than the plug. That is all I am saying. This piston is about two (2) main jets too rich. Runs great. But could be better. Plug reading looked great. My point is using the piston is more accurate. You can see how the chamber is burning and how the exhaust ports are defined.

[dajogejr]

You are exactly right...I'm impressed.
Too much oil can also cause that much carbon build up...as well.

I can't tell for sure, but it looks like some blowby on the bottom side of that picture, could very well be a smudge of dirt or oil from handling the piston...however...

Fine tuning by piston burning patterns is the tops in tuning. However...spark plug reading IMO is 98% as good, if you know how to properly check a plug for heat, timing, etc...

Some will argue that tuning by Wideband 02 sensor is the best, I would only agree if the sensor is permanently mounted and you can keep the monitoring device on the bike/cart as it runs. If you only tune by 02 at the dyno, temps, altitude, rider weight (load), etc. can change the reading....

You're obviously gonna pull plugs at the location you're riding at...you MAY be able to peak at the crown, but not always...

Good info Tony....very nice!!

[fulltiltrider]

Yes, reading the piston is very accurate but most of the guys on here are weekend worriors and trail riders. I wouldnt encourage the backyard mechanic to try to tweak thier machine in only to blow it up in a week. Trust your plug and the seat of your pants