2011 ec125 Six Days compression?

[rosco]

Does anyone know what stock compression would be on the 125's. I know the 300's run around 175lbs. I'm only getting about 135lbs on this new 125. Seems pretty low to me. Pulled the pipe, the cylinder and piston look like new. Thanks! Ross

 

[barossi73]

Check your tester on another bike and compare or retest.comp guages are notorious for variation and a vague tool for 2t.
If you have the pipe off,look for signs of blowby on piston.ie signs of combustion below the rings,the piston crown will look burnt/blackened.below rings should be pretty clean,except for blackened area just below rings on the exhaust side as its exposed to burn when port is partially open and rings are at mid port.
If its blackened way down further combustion is getting past rings.
Looking at a piston that i pulled out of my 200 at 65hrs the 'normal' blackened area is more or less horizontal and extends approx 10mm below the bottom ring on the exhaust port face.
Note.the piston was not worn out,comp was still good,no blowby.in hindsight could have run 100hrs easy(200)
You can slowly turn piston over with flywheel by hand with spark plug removed and view thru exhaust port

 

[Elvis74]

The squish on the 125 should be around 1,2mm


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[Zrt1200]

More than likely your squish is out to lunch. I just did my 200 yesterday. My squish was 1.5mm to 2.5mm / .060" to .100" I recut it and now its at .045"/1.14MM.

 

[rosco]

This is a new bike, piston and cylinder cross hatch look like new. Just trying to find the specs on compression. Surely these things must run more than 135 lbs. of compression. Thanks for the info but I was just curious if anyone has ever checked the compression on a good running 125 and what to expect from one.

 

[Elvis74]

No, sorry, I never checked it. When I think I have a problem with mine, I just pull the cylinder and check and or replace everything.
By the way, I am here one of only a hand full 125/144 riders. ;-)


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[Zman]

I just checked our 2002 125 and it is 150 PSI and I am wondering if that is low. I did notice 130 PSI cold and 150 PSI warm.

 

[rosco]

Thanks Zman! That's the kind of info I was looking for. So is your bike running ok with that type of compression? This bike just runs like crap. Jetting doesn't seem to make any difference. Powervalve is working fine. It almost acts like it is hitting a rev limiter. Starts good, idles good, runs fine up to about 1/3rd throttle and then starts to dog out on power but will continue to rev to about 1/2 throttle or a little higher and then starts to cut out like a four stroke banging off of the rev limiter.

 

[Elvis74]

Give us some more information. Which jetting do you run. Gasgas has for some markets pipes with a catalytic converter, check with a wire or so it your pipe is free and open. Is everything else in good condition? How about the sealing rings of the crank shaft.


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[Jakobi]

Thanks Zman! That's the kind of info I was looking for. So is your bike running ok with that type of compression? This bike just runs like crap. Jetting doesn't seem to make any difference. Powervalve is working fine. It almost acts like it is hitting a rev limiter. Starts good, idles good, runs fine up to about 1/3rd throttle and then starts to dog out on power but will continue to rev to about 1/2 throttle or a little higher and then starts to cut out like a four stroke banging off of the rev limiter.

Usually low compression will show its face at low rpm. Hard starting, poor idling, weak response off idle.. but will still run around at higher rpms a-ok.

 

[rosco]

So I ordered a Wossner piston kit for it last week. Went to put it in today and noticed quite a bit of difference in the two pistons. The stock piston[I hope its stock] has a flat top and no window on the intake side. The wossner has a slight dome to it and has a window on the intake side. SO now I am dealing with a clearance issue between the top of the piston and the head.
So has anyone ran a wossner on their 125 and if so did you run into this same problem? Also I see this thing has a Vesrah rod on it. I didn't think anything came stock with a Vesrah rod.

 

[Elvis74]

The piston with the done is for the older models, the current one have a flat top!


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[barossi73]

Does the old piston have any markings on the crown that could identify it?

 

[Elvis74]

This is how the current piston looks like

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[rosco]

Thanks guys! I'll have to order in another piston. It appears that it has the stock piston in it but you can see where it got scored on the ex. bridge. I'm guessing that was some of the reason for the low compression reading. So are you guys running about a 1.2mm squish clearance on the 125? Hopefully I will have something figured out on the running by the end of the week. I have a buyer that has been very patient on me to get this thing running right.

 

[rosco]

So are you guys using the stock GasGas piston as a replacement or have you found another option?

 

[rosco]

Also curious if the Vesrah rod is stock or if someone has put a rod kit in it.

 

[Elvis74]

I run woessner pistons in mine.
In the 125 I run the stock rod, in my 144 I have a wisco rod from Yamaha YZ with a Yamaha YZ piston.
Stock parts are ok for a not tuned motor.


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