[Blueflag]

Engines looked leak free. Exhaust systems were sound. wiring good. *IF* the bilge had been pressure-washed, you’d be hard-pressed to know these were 12 year-old motors.

Never done a compression test on a small displacement 2-stroke; only 4-stroke automotive - mostly 4 cyl.

Is it as simple as removing one plug, cranking the engine for 5 seconds and timing the leak down? (then repeating fore other cylinders)

I don’t know the proper leak curve ;-)

[Don W]

Because 2 strokes open the both the intake and exhaust ports as they approach BDC, you have to accept only the peak compression reading. Leakdown tests are difficult, to say the least.

Do one test “dry”, then squirt some light (sae20) oil into the plug hole and test again. A significant difference is obvious and telling.

HTH.

[steve86]

I'm still running the original crank seals on 70s and 80s and 90s two-stroke trail bikes. Been lucky that way. Original carbs and jets, too, mostly.

On the two stroke upper cylinder compression tests (these are singles), we always remove the plug, put the plug cap back on the plug, ground the plug, and kick over with the throttle held wide open. People have different practices regarding warm vs. cold motors -- just be consistent.

You can find Youtube videos showing leakdown tests -- they aren't that difficult. I've actually never bothered to do one.