1999 Mercury XR6 150 High Compression one cylinder?

[SteuryLover]

We were out the other day and noticed we were real low on oil and the alarm was not going off. We put in oil and drove back and pulled the boat out. I did a compression test to be safe. The motor runs fine, but I have high compression in one cylinder. My compressions #s are as fallows. 120-120-120-120-130-112. The motor runs great and starts right away. I looked in the plug holes and everything from what I could see looked good. Why would one cylinder read high? Is it time for a good decarb? Thanks for your time guys.

 

[vegasphotoman]

Re: 1999 Mercury XR6 150 High Compression one cylinder?

could be carbon build up,

is that the bottom cylinder that's the higher compression? knowing cyl number could be helpful to the knowledgeable outboard guys

ps 10% deviation is OK.......you are at an 8% deviation thereabouts with the 2 cylinders (112lb and 130 cylinders)

also a bit more oil on the cyl walls could cause a higher compression reading perhaps? (that is an educated guess)

 

[SteuryLover]

Re: 1999 Mercury XR6 150 High Compression one cylinder?

could be carbon build up,

is that the bottom cylinder that's the higher compression? knowing cyl number could be helpful to the knowledgeable outboard guys

ps 10% deviation is OK.......you are at an 8% deviation thereabouts with the 2 cylinders (112lb and 130 cylinders)

also a bit more oil on the cyl walls could cause a higher compression reading perhaps? (that is an educated guess)

Thanks for the response, the middle port side is the 130psi, the bottom port side is the 112psi. The motor runs great, no issues staring or WOT. I will do a decarb this sweek and see what happens., thanks.

 

[Dukedog]

Re: 1999 Mercury XR6 150 High Compression one cylinder?

Tha 130 I wouldn't worry to much about but I would check tha 112 after each trip just ta be safe...............Its probably ok but never hurts ta check.

 

[SteuryLover]

Re: 1999 Mercury XR6 150 High Compression one cylinder?

Tha 130 I wouldn't worry to much about but I would check tha 112 after each trip just ta be safe...............Its probably ok but never hurts ta check.

Good point on the low cylinder.