All I can tell you is what it isn't...

What it is, motor runs like a champ, and then drops a cylinder, runs on two. Fuel restriction? Glummed up carbs? Nope, and nope because... I can turn the key off, then restart and it jumps up and runs perfect again. Maybe for a while, maybe not, but every time it falters, restarting gets it going strong.

I'm thinking a coil is breaking down, but dang that's weird, anyone have any other thoughts before I start chasing this down?

Had almost the same problem on a 3 cylinder 2006 50hp Yamaha. Was ready to pull my hair out because ignition would test good. Finally caught it dropping the cylinder and test indicated the power pack. This one had a very expensive power pack.

I'll start there Gary, thanks.

I have a 90hp Yamaha 2 stroke and would like to be able to recognize this problem if it arises. Pat, how do you know it is dropping a cylinder and running on two? Does it start running extremely rough and puttering?

one of the thermostats are either clogged or not opening and one bank is overheating causing motor to go into limp mode. take stats out and see what it does.

Leanin post this motor is an inline 3 cylinder. When a Yamaha goes into protection mode it will barely get above idle but it runs smooth.

Pretty sure it's a coil breaking down, the thermostats were yanked the day I rigged it. That motor sucks way too much mud through it to have anything restricting water flow.

Had a 2 week old CDI coil pack do that to me on a rude v4. Hooked up and zip tied the trigger on an old timing light so I could watch it while runnin. Figured out which cylinder was dropping, switched packs around and she revealed herself.