03 yz 125 compression

[yamahammer01]

hey guys, i did a compression test on my yz 125 i opened the throttle and kicked 5 or 6 times, got a 120 psi. is that good or bad, and i was also wondering if i were to either mill the head, or deck the jug. which one is best and how much can i safely take off.

[Aus_Rider_22]

That's a little low I think. I would be looking for a 150 sorta number.

I never measured the compression on my YZ so I can't really offer any advice sorry!

I am sure the other guys will chime in

[Faded]

Altitude will have a negative affect on cranking compression numbers... If you're at altitude your reading might seem low; a 125 that blows 150psi at sea level is only going to register approximately 129.5 @ 4000ft.

But, your bike @ 120psi does seem low. When was the last time the piston/rings were replaced? Milling the head/cylinder isn't going to do much good on a worn top-end...

[ossagp1]

Taking some off the bottom of the cylinder will help with low and midrange hit, MAY not require any head mods as far as squish band is concerned, but costs on top. the 134-144 sounds better to me really.

[yamahammer01]

i know that milling wont help on a worn out head...i kinda put 2 ?'s into one there sorry. i just wanted a little advice on milling sience i was gonna replace the piston and ring, and i woulda had it apart at the time, i ordered the piston kit today, i would rather spend 90.00 than god knows what. thanks for you help and ossagp1 u mean go big bore? thanks again fellas.