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My advice is that you check your points and try to get a stronger spark, install new spark plugs, check compression on both cylinders, and otherwise pursue the notion that one of your cylinders isn’t firing well when your motor is under load.
Thanks Jim, this is exactly what the problem is, lack of spark or low spark in forward for the top spark plug. The funny thing is that it works perfectly in the test tank, but in the water back to low power. What I found was the RPM when in the test tank was like 5500rpm in forward or reverse. But in the lake, 3650 max forward and 4300rpm in reverse.
Take your spark plugs out and look at them. If it’s running on one cylinder, the plug not firing will be wet with the gas/oil mix. These motors will run pretty smooth on one cylinder.
Thanks Larry, the top plug is wet (especially after being in the lake), so I have (with all of this help) found that the top plug is not sparking enough or is arching out under a load.
just some interesting reading on Merc ignition
https://wrcoutboards.org/wp-content/uploads/2021/02/The-Phase-Maker-CDI.pdf
Thanks Crosbyman, I am in the process of reading this, it is very interesting to me. My Merc appears to have a standard magneto setup. So, I guess I will be cleaning the points, checking the plug wires and replacing the plugs. Thank you all for the help on this so far, I feel that I am getting close now and hope to update this and say that it is fixed soon. I will keep you all posted and thanks again!
Gerry
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from early 70s upward Merc was evolving to electronic ignition ex: with stator CDI ignition under control of a trigger coil ( no mechanical points) .
around mid 70 they had phase maker ignition a bit of a mix of CDI and points MAKING contacts to fire the points. Normal magnetos usually OPEN their contact surfaces to generate sparks but PHASE MAKER closes the points to fire.
here is a good read on Merc ignition by M.Mohat
https://wrcoutboards.org/wp-content/uploads/2021/02/The-Phase-Maker-CDI.pdf
https://wrcoutboards.org/wp-content/uploads/2021/02/Generator-Coils-Explained.pdf
Joining AOMCI has priviledges 🙂
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