1998 kx250 compression spec

[frankenbike]

I tested compression on my 98 KX250 and it is 172psi
The Clymer manual gives a range of 110 - 177psi
I thought I was good until I read in Eric Gorr's handbook that
250s should be much higher (i think it said 200 - 250psi).
What "should" it be?
This is my 1st 2stroke, and it has tons of power...very easy to pick the front end up in every gear, and it doesn't seem to bog down at all, but then again, I am coming from a 250 4stroke.
Also, another glitch is that I bought this bike used and it has "Tom Morgan Racing" cylinder and head mods (it claims that this will increase the compression ratio). I haven't had any luck finding out from them what the compression should be.
Any help would be appreciated.
Brian

 

[frankenbike]

thanks.

 

[Rockey5000]

The OEM manual says it should be 175

 

[KXTodd]

Left a dangling thread huh? hate it when that happens ;)
Mine was 210 psi after I put the last topend in, just got the lower end done and should have it back together soon, I'll let you know what it is when I get it back together.

 

[bigred455]

Fresh top end after break in stock compression.My 00 kx 250 reads 235.I have just under 50 hrs on mine and my reading is 225.I still have great compression,but it will come apart after 1 more ride.

 

[frankenbike]

Thanks yall !
I plan to do a top end job after the race this weekend. After that I'll have a baseline for compression... (assuming I do it correctly, since this will be my first top-end)

 

[KXTodd]

Broken in now, my bike is at 210 psi, same as last time I did a top end. :thumb:

 

[frankenbike]

In case anyone was wondering, I did the top-end and only measured 185 psi. It "felt" like much more compression though. After talking to Eric Gorr, I found out that I needed a flat top racing piston because of the head mods done by TMR. He said that I would have low compression with a stock piston...sure enough, I did.
Just thought yall should know in case you get a bike with head mods.

 

[TRX55]

Hey, couldn,t help reading this post, my cylinder plating is getting kind of thin and showing some alluminum especially around the exhaust port. I've been putting the replating off for a little while and just replacing the piston and rings every 50hrs. or so. I did do a compression check on it soon after a recent rebuild and my reading was about 118psi, if this is really low for my 250 what should i be getting? I would really like to know if anyone has any experiences with the 95kx250 and if replating would noticably boost the bottom end any. Thanks for any info...................