2005 Yamaha 70 running on 2 cylinders

[dhearn0513]

Engine has been spitting and sputtering when throttling up. Determined that it’s running on 2 cylinders by pulling wires off and listening for change. The culprit is # 3. The engine sat for a few year so first thing I did was open the carbs and clean them out. The cylinder in firing across spark gat tester. Spark looked alittle weak but I don’t have anything to compare it to. I changed coils around and the prob stayed with #3 so coils fine. I replaced fuel pump thinking maybe it was dumping fuel into cylinder being it gets its pulse from #3. Anyone have any other suggestions. Compresson is #1 100 #2 103 #3 98

 

[SaltyDog727]

Does your buzzer work? If the engine is on and you pull the lanyard, does the buzzer sound?

I had a similar issue with a 2004 Yam 70TLRC 2 stroke. It would start right up, idle fine, but would violently shake and not get on a plane with the throttle down. Checked spark, compression, fuel, cleaned carbs and still had same problem. Turns out it was actually a bad oil sensor. I didn't know it was the oil sensor because my alarm buzzer was also bad, so it never went off. It actually put the engine into a "guardian" mode because it thought I was low on oil.