Yamaha 9.9

[Bob G]

I have a 1994 Yamaha 9.9 which changes RPM on its own with out changing throttle position. The motor is now misfiring on occasion to the point where it sounds like it will stop and then it will run fine again. I have had the carborator cleaned and adjusted,checked fuel filters, changed the fuel lines, checked the fuel pump diaphram and check valve,run Seafoam through the system. Pressuizing the bulb does not help whenit misfires. One of the plugs is blacker than the other but is not fouled. I don't know what else to do other than change out the CDI unit. Could that be the problem? Any other suggestions?

[FishFinder]

Bob,
Have you run a compression test? You pre-mixing or ?? Does it have separate coils for each cylinder?

You could…
1) Run a compression test on each cylinder

2) If the compression looks ok I would swap coil packs around and see if the problem follows the coil.