Poor Compression 9.9HP Merc 2 Stroke

[Luv_Fishin]

Hi
I have a 1999 Merc 2 Stroke 9.9HP that was under river water for 7 days. It was not running when it went under.
It will run but I believe it could use a carb overhaul, fuel pump diaphram and accelerator pump.
Compression checks out at 75# in both cylindars and should be 110#.
Any idea what could be causing the compression loss?

Thanks in advance for any advice.
Cheers
Rick

 

[Badburn]

Re: Poor Compression 9.9HP Merc 2 Stroke

Rust maybe? I'd run it a bit, and then re check it. My merc 15 shows 80 # on the compression test, and the forum is telling me that's decent.

 

[JB]

Re: Poor Compression 9.9HP Merc 2 Stroke

Ahoy, Rick.

Welcome to iboats.

Where did you get the idea that you should get 110# on a rope start outboard??

You should get a close (10%) match among the cylinders. 75-75 is good compression.

 

[Luv_Fishin]

Re: Poor Compression 9.9HP Merc 2 Stroke

Thanks a lot for the info guys. That gives me hope. My factory service manual showed either 110 or 115# compression for this motor.

 

[Luv_Fishin]

Re: Poor Compression 9.9HP Merc 2 Stroke

Hi all; Have some good news. Went out to the lake yesterday and ran the motor for 4 hours at various speeds. It now seems to run just as good as before it was submerged (not running) for 7 days in the river. Long story but a good one!
Compression is still 73#'s on both cylinders.
My Mercury Factory service manual which covers 2 stroke motors from 6 to 15 HP quotes "Normal Compression at 115 to 125 PSI. The difference in compression readings between each cylinder should not vary more than 15%. If compression varies by more than 15% or compression for both cylinders is less than 100psi (685 kPa), the powerhead should be disassembled and inspected."
Should I be concerned???
Cheers to all and thank you for advice.
Rick
Luv_Fishin