Another 1985 Merc 60 issue.

Todd 1669

Seaman Apprentice
Joined
Feb 21, 2009
Messages
46
This motor has a bit of a history with this issue but last night it seems to have come to a head.
In the past the motor starts fine and although the low idle has been rough it would idle downriver to the mouth of the lake (a mile or so) and then go to full power and run at 27-30 mph with no problem. The issue comes when shutting it down for a while (hour +) and restarting. Prior to last night it would intermittently refuse to run at full power with throttle open. The motor wouldn't miss and it ran smooth, just low RPM/power. It would feel like running about half power/rpm and every few seconds it would jolt/spark like it wanted to jump to full power. Eventually it would kick in and then it would run fine wide open. Almost like it had a low and high power setting and high just needing some coaxing to come to life.
Last night I couldn't coax her past the half power and best it would do was ran 12 mph no matter what I did. It did jolt a few times like it was trying to get up to full but it never did.
In neutral it revs up just lovey and gets max rpm. In reverse it seemed to get much higher rpm than in forward although the water was pretty choppy so I didn't run it long in reverse.
Compression check last month was 105 (+- 2) in each cylinder but I will recheck them tonight. Spark jumps 3/16" gap but again will recheck.
Ive attempted to do the troubleshooting from CDI website and stator/rectifier/coils and power pack checked ok although my skills and equipment are fairly limited.
Motors a 1985 Merc 60 3 cylinder SN 6461967.

Any help is much appreciated.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,453
Spark should be able to jump a 3/8" gap with ease.-----Perhaps run with a timing light to see if you can find the cylinder with spark issues.----Perhaps run after dark to see if spark is leaking somewhere.
 

Todd 1669

Seaman Apprentice
Joined
Feb 21, 2009
Messages
46
My mistake. I meant 3/8" gap. It jumps that easily.
I'll try running in the dark.
 

Todd 1669

Seaman Apprentice
Joined
Feb 21, 2009
Messages
46
I ran it in a barrel last night and didnt see any spark leak but only ran it at idle. The symptoms don't appear unless in gear at 3/4 to full throttle.
By using the timing light I assume you're talking about just looking at the light pulse to look for changes when symptoms appear. Not checking the timing itself. Again its going to have to be at the throttle
There should be a whole forum tab for these mid 80's 3 cylinder mercs.
 
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