2005 mercury 50 horse running on one cylinder

rhays001

Seaman Apprentice
Joined
Mar 1, 2009
Messages
32
Have a 2005 50 horse mercury 2 stroke model 50elpto 3 cylinder that is running on the top cylinder only. This motor was just bought and I do not have any prior knowledge of how it ran before. Pulling the plug wires on two and three give only a very small difference. Stalls immediately when top plug wire is pulled.
-it has spark on all 3 cylinders
-pulling plugs, all three are wet..
- checked to ensure all three carbs are getting fuel and not flooding.
- set idle screws to 1 1/2
-new plugs- no difference.
-It starts and runs and idles.
-Compression 110 on all 3
-switched the coil positions, no change problem stayed on top cylinder.
-Pulled the carbs- all very clean, blew them out and reinstalled- no difference.
-switched top carb and middle carb - no difference only top cylinder is running.
-pulled the reed valve block, all are clean and appear to be shutting tight.
Any ideas? The motor is very clean and looks like it has not been used much,,, maybe 200 hours.
could it be Electical and even though it shows good spark on all three cylinders still be an issue? I looked all the wires and all are connected.
thank you very much for your help.
bob
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,309
Sounds strange.
Likely not your issue but I’m aware that some modern outboards can shut down cylinders at low rpm for economy. Perhaps unlikely in your case and only firing on one of three ?
 
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