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I recently did a compression test on my 97' KDX 220 and was wondering if 100-105 psi was any good?
I was told a new piston was put in in 2004, but the view of the piston through the spark plug hole shows a good layer of carbon build up
The bike was able to hold the 100-105 psi for a while

your knowledge is greatly appreciated

That would mean it was time for a rebuild in a 200 but I'm not sure in a 220. However, that sounds way low to me for any 2T engine. Hopefully someone with a 220 service manual can chime in.

I have the manual, I'll look it up and get back to you

okay, thanks

For an H 200 the book says about 98 to 151 is usable but I would say anything under 125 or 130 is time to order some parts.

On a side note, no engine cylinder will hold compression. The gap in the rings will let the compression go by as soon as the piston stops moving. Even as it is moving the compression is getting thru the ring gap. Staggering the rings helps slow it down but it is still happening. This is why a compression testing gauge set up has a check valve in it. If you check the compression and the gauge slowly goes down then it is a bad compression tester and not anything to do with the engine. Have you ever pulled a spark plug out and heard the air hissing out?

The compression tester was not in the best of condition, but it only dropped 4 psi in 15 minutes.
I'm going to replace the piston regardless, when I pulled the pipe off I could see that the top edge of the piston above the rings had almost small chips in it, I could almost catch my finger nail on them. Also the piston was looking pretty darkened from carbon.

Thanks for all the help

Compression test is throttle held open, and kick until the gauge stops rising. Does sound like you need a top end regardless, if there is visible damage on top of the piston. You'll also want to investigate what may have made those chips in the piston while you have it apart. Bottom end bearings and such.

I held the throttle open and gave it 3 or 4 kicks until the gauge didn't rise anymore

I will check the bearings and connecting rod and stuff when I have it all apart