96 Mercury 115 2 stroke intermittent loss of one cylinder at 3/4 speed

[ImPatience]

I have a 96 Mercury 115 ELPTO 2 stroke 4 cylinder At full throttle it runs great and all four cylinders are definitely firing. At 75-80% throttle, it seems like one of the cylinders will intermittently not fire. There is a momentary change in sound and loss of power, and then it starts working again. It just keeps doing this over and over when you run at that speed. It happens like every 3 seconds This has been happening off and on for years and I am finally tired of it as it is doing it fairly regularly right now. I'm not sure how I can figure out which cylinder it is, because I won't be able to get up to that speed if i disconnect any of the spark plug wires.

Any ideas?.

 

[racerone]

Hook up a timing light and lay it on a seat.-----Observe the flashing light.-----Steady flashing light means all OK.----Black spots means you have found a problem cylinder.----Test all 4 leads.