'89 35hp merc twin lossing power

CHAWK46

Seaman Apprentice
Joined
Jun 29, 2008
Messages
45
My 35 starts and runs great the first time in the lake every year. Leave it for a week, it may start and run fine or will seem like it's running on 1 cylinder. Take it down the lake and it may go back to full power like flipping a switch. Tried pulling a spark wire when running bad, no difference. Pull the other one and still runs the same way. Thought I might have had a coil getting moister but the plug wire test ruled that out. I'm thinking of tying a wire to the power wire on the switch box so I can check to see if there is a difference in voltage between good and bad running.

Any ideas would be appreciated.
 

CaptnKingfisher

Petty Officer 1st Class
Joined
May 14, 2017
Messages
259
Tried pulling a spark wire when running bad, no difference. Pull the other one and still runs the same way. .

Good idea trying a cylinder drop test but I'm confused at your explanation and interpretation of your results. did you do this with motor running? If you pull a plug boot off the sparkplug with motor running and don't notice a drop in rpm, that means that cylinder wasn't firing. (Use heavily insulated pliers by the way).

If this is the case, then you've identified the problem. Now we just need to identify whuch ignition component is failing. Am I interpreting your 1st post correctly?
 

CHAWK46

Seaman Apprentice
Joined
Jun 29, 2008
Messages
45
Ok, I start the engine, runs bad. Shut it down and remove a plug boot, runs the same. Shut it off, reinstall plug boot, remove other plug boot, runs the same. The reason I'm thinking ignition is if you take it down the lake when its running bad, it goes from bad to full power in less than a second. Like I said, when I put it in the first time every year it runs fine.
 
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