I have twin 1996 Mercury 225’s (225425SD 0G350987) and loosing RPMS in the port motor. Its carbureted and oil injected and it ran fine until recently. I first start the engine it runs like crap (spitting and coughing) and takes some time to warm up and idle ok. Once at speed it will be running at 3700 RPM then it will drop down to 3300 RPM for about 5 seconds then back to 3700 for about 3 mins. It just keeps doing this cycle. I have checked the plugs and wires, they seem snug. I changed the fuel filter and fuel lines from the tank to the motor. After reading some posts it sounds like it could be a stator or trigger. How would you test these. Also could be a power pack on one of the cylinders. How to test just one.

If you purchase a service manual you can test everything but the power pack. The power pack does not have an accurate test.

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