Low Compression + Carbon Buildup

[Ally008]

Hi, I'm running a Mariner60 outboard. I got it serviced last week and the guy told me that the compression was low in cylinder 3 at around 90lbs. The other two were at 115lbs,117lbs. He didn't tell me what the cause was, but did say that the engine was running nicely regardless of what his tests stated. I've read that compression should be around 100lbs and all cylinders should be within a range of 10-15lbs of one another. Mine obviously falls outwith these parameters. Should this worry me?

I know nothing about repairing or maintaining outboards so I dug around on the net and came accross the process of decarbing.

First question is, will this help? If so, I don't fancy dismantling the carb to soak it. Is there a suitable fuel additive available in the UK? Yamaha sell ring free fuel additive in the States for outboards but not seen it anywhere here.

Any help would be most appreciated!

 

[Matt]

Decarbing refers to removing carbon, not rebuilding the carbs.
If you think carbon build up could be the issue, quicksilver/mercury powertune is designed specifically to remove carbon build up.

 

[Jon Fuller]

I think, if it were my motor, and the slightly lower compression on one cyl was the only sign, ie, motor was still mechanically quiet, and ran nicely, I would continue using as normal, mebbe just listening out for any changes in it's behaviour or sound.

Out of interest, has the motor been stored(unused) over the winter prior to this compression test, or was it done soon after some regular use?

 

[Ally008]

Thanks for the replys, yes the boat had been stored for almost 5 months without being started. Do you think this would have affected the results?

 

[Jon Fuller]

the boat had been stored for almost 5 months without being started. Do you think this would have affected the results?

It certainly could do.