High compression bottom cylinder

[NB Boater]

Just picked up a 70ETLF. Tried a compression test on it (cold). Top Cylinder 110, Middle 115, Bottom 175. I am aware of several ways to lose compression, but can anyone tell me why the compression would be so high?

[99yam40]

did you run the tests more than once to see if they all matched,
gauge problem is all I can think of off hand

[DennisG01]

On a 2-stroke? Not really anything that could cause that that I can think of. Other than an exhaust port that's nearly blocked up... but that would cause other, more noticeable problems. I would lean towards gauge issues as mentioned above or user error... although I'm not even sure how one would "error" into it being higher than normal.

[ausnoelm]

Best guess you did something wrong or the gauge is now faulty, that number is higher than when the motor was new, so, there is either some weird mechanical issue, that cylinder is full of oil/fuel/water, the gauge is a dud, or somehow, “something” went wrong using the gauge on the bottom cylinder.

[99yam40]

would a oversized cylinder/piston cause that much increase?
what about a higher dome on piston if that cylinder got reworked?

[ausnoelm]

Oversize no increase in compression, a dome piston would, but, even the most inept mechanic would see a dome piston when the other ones are flat, never seen a domed Yamaha piston.

[99yam40]

larger volume ,same stroke, I would think it would increase the PSI, but a small amount for 10 - 30 oversized.
you never know what someone would do to a motor if they are not keeping it.
he did say he just got the motor, so he probably has no clue what was done to it.
I was just trying to come up with anything that might cause an increase