1979 Mercury 115 2 stroke Half Power Full Throttle

[Powza]

1979 Mercury 115hp 2 Stroke distributor

The other day I was out on my boat everything fine until I was about to head back. When I hit throttle all the way I lost half my power and couldn't get up to planing speed. I shut it off and turned it back up and still same issue.

Possible things I was thinking of:
Replacing the old throttle cables. They seem very stiff
Carbs clogged? I cleaned the cards and with new kits 4 months ago.
Removing the propeller to see if anything got stuck.
Dirty spark plugs?

 

[racerone]

Post the results of these tests.-----Compression test first.-----Then does spark jump a gap of 3/8" or more on each lead, yes or no ?-----Has impeller been replaced ??

 

[Powza]

I'll do more testing soon. I pulled the the spark plugs and 5 out of 6 were wet. The one from the 2nd cylinder was completely covered in build up. Looked awful and could be the issue. Cleaned them all off put them back in and starts up and idles like normal. Plugs are 3 months old.

 

[racerone]

If you answer / respond to questions the issue with the motor is quickly determined.

 

[Chris1956]

3 month old plugs covered in build-up is quite unusual. If your compression is good, I would suspect carb issues. Also, check spark plug wires for arcing to ground, when running. Those old yellow tiger tails do not last forever.

 

[Powza]

Did a compression test and found cylinder 2 is at 95 PSI and the other 5 are 120 PSI

 

[racerone]

Remove the upper bypass cover in the side of the motor to have a look at the #2 piston.-------This sounds expensive.

 

[Faztbullet]

Likely still has the idle stabilizer hooked up......

 

[jimmbo]

if you have access to a fiber optic camera, a great time to use it.

 

[Faztbullet]

If it had aluminum build up on plug no inspection necessary as it needs to come apart... You have the ADI or distributor ignition as 79 was year you could have either.