'89 DT75 dropping a cyl at speed

[2014DF25ARS]

You don't say that you replaced the plugs... I have a 65HP Evinrude 3-cyl that was doing the same thing - randomly dropping one cylinder above half throttle. I could back off throttle and it would accelerate. After looking at most stuff you're looking at, I was about to replace a coil pack, but they're kind of expensive. So I decided to replace the plugs first, though all three looked similar and fine to me. No more problem. Not saying it's a sure thing, but maybe worth doing.

[Flatsboy]

Thanks for the reply, manual still not here but good advice.

[Solarman]

If the plug wires are same length, could try swapping coils between two cylinders, and see if still the same?
Before swapping, could use timing light to see if losing spark on any plug when this happens, then swap coils and repeat the test.

There may be a flow switch combined in the temp sensor that may cause motor to limit at 3k rpms on your model, but because motor isn't overtemping, it might not set off alarm?

Also the gear counting coil could be acting up at higher rpms?

It might be better to wait for the suzuki manual before jumping the gun. Then you can test those items by the manual.

Good luck, post back when able to let us know how it's going. And if you find anything.

[Flatsboy]

'89 DT75 ran fine last fall, now dropping 1 cyl above 3,000 after 1 minute running, let it idle and it will run up again then drop a cyl again. Will run at 3,000 all day on all 3. Neither oil or temp alarm sounds off when cyl drops. Drained carbs last fall, new gas and oil this spring.

Since this happened I did some maintenance - high numbers on compression, all within 2 lbs of each other, replaced oil tank filter/flow sensor, replaced impeller. Took old sensor apart and the screen was pretty clogged with gunga, drained and cleaned oil tank, bled pump, rebuilt fuel pump.

Today I ran it thinking maybe the clogged oil filter/sensor was it but no go. When the cyl dropped I ran it on two back to the dock and shut it down at speed (barely on plane). Top spark plug was hot but noticeably cooler than the bottom 2, still looks like it's firing but dirtier than bottom 2.

Leaning towards a coil. Have service manual coming but was hoping someone here can clue me in on how to test the coils or have another idea. Was a dlr for Merc and Yamaha so Suzuki is new to me. Seems like a great engine, just finding my way around it.

Thanks in advance!