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mercury 50 horse running on one cylinder

R

rhays

Member
Good afternoon, I have a issue that I can not solve. 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 does have spark on all 3 cylinders
-pulled 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, runs and idles, just on #1 cylinder.
-Compression 110 on all 3
-switched number one and two coil positions, no change, still running only 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 still 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 with a trigger, even though it shows spark on all three cylinders still be an issue? There is not a switch box on this, all the wires from the trigger go to the coils. I looked all the wires and all are connected with nothing burnt.
thank you very much for any ideas.

 
Sounds like wires from switch box to coils are mixed on #2 and #3.-----Switch # 2 and # 3 coils WITHOUT switching any of the wires as a test.
 
Thank you for your help
my apologies, this year (2005) does not have a switchbox.
the optical sensor has 4 wires coming out of it that goes into the wiring harness and then out to 3 four prong plugs that goes directly to each CDM coil module.
Thank you again for any help.
 
Thank you sir, i will update the serial # as soon as I get back to the boat.
Still running on only one cylinder. If I pull the number 2 or number 3 plug wire when running it make a very very small change rpm and barely noticeable difference. If I pull number one, it immediately Stalls. I’ve read many of the forums and tried switching the cmd coils, cleaning carbs, checking the reed valves, ensuring gas is flowing through the carbs.. checking for spark etc... this one has me baffled.. could it be an optical sensor or a bad cdm coil, is there any good methods for testing them. I pulled the flywheel yesterday and do not have any broken wires or magnets, the magnets all seem to have 1/8” between them.
Thank you again for any thoughts .
 
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