I have an early-mid 1990s (not quite sure) Mercury 150, carburetor engine. I have no spark on cylinders 2, 4, 6 at idle. However, when I rev-up the engine, the engine smooths out and I get spark on cylinders 2, 4, 6. I checked voltage going to coils for 2, 4, 6 and there is almost no voltage at coil UNTIL I rev engine, then voltage increases and I get spark. the engine obviously is running and it affects only that one side and not cylinders 1, 3, 5? they are firing normally. PLEASE help me find a solution to my problem so I can get back out on the water. Thanks and God bless!!

It could be stator, switch box or depending on model idle control module.
The service manual will give you test procedures for testing ignition system but you will need to get serial number to identify which model you have.

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thanks for the reply! any idea which it is most likely? is the switch box the same as the power packs? lastly, i know my mercury 150 is between a 1987 and 1996. the sticker on lower unit has a serial number, but it also says "150efi" which it is NOT so i know it is wrong. thanks again and God bless!!