Generic compression question on two strokes

[heyblue]

If a two stroke engine runs fine but has compression of 115 115 90, is there reason to be concerned or is the difference within acceptable numbers?

 

[Chris1956]

Well, that low number is a bit lower then we like to see. We would like +- 10%. However, depending on how old the motor is, you might decide to just run it...Normally motors with damaged cylinders have compression numbers of zero or 30 PSI, so your low cylinder is still in reasonable shape.

 

[robert graham]

You could re-check it with a different compression gauge....you may also have some carbon-stuck piston rings...might do a de-carb by running a tank of fuel with the "carbon removal" dosage of Yamaha Ringfree. Afterwards re-check compression for any changes/improvement in readings...

 

[jerryjerry05]

Yea a decarb is needed.
Yamaha Ring Free, Mercury's Powertune or OMC Engine Tuner.
. Removing the plugs and spraying into the cylinders. I let it soak for 2 days
I don't mix it in the fuel as I don't want it to strip the oil that's on the bearings.
I do shoot it into the carbs but not a bunch.
That 25# difference is not good.
If my cylinders had any more than 5# difference I'd be looking for a reason.
You removing all the plugs when you do the test?

 

[racerone]

Remove the exhaust covers ( if equipped ) and inspect that bad cylinder / piston.------They generally do not heal themselves if bad !

 

[Chris1956]

If that motor is a direct charge motor, it should have transfer covers on the starboard side. They usually come off easy and you can see the cylinder and a lot of the piston.

 

[racerone]

The big loopers also have a cover on the port side of the motor.