I have a 1986 Yamaha 115 2 stroke that has always been a good running motor, until now. It cranks easy, but it is down on power and when I get it up to 4000 rpm the motor will start to surge up 1000 rpm or so and them back down not running smoothly. It is also going through much more gas than usual. The motor has 120 psi on 3 cylinders and 130 on the 4th. The pulsar coil charge lighting coil are all within spec. I swapped 4 used ignition coils for the coils that were on it and it still runs the same. I can pull the top two plug wires and it will crank and run on the bottom two cylinders. I can also pull the bottom two plug wires and it will run off the top two cylinders. The Carbs look clean, I know that doesn't mean anything. It does look like it is putting excess un-burned oil on top of the water. Before I swapped the coils it would only run on the bottom two cylinders.
It idles like it always has, not silky smooth, but idles. I have to think that the trigger is working since it runs on either upper or lower cylinders. I have checked and gas is getting to both carbs. Plugs are new, and I just ran a can of seafoam through the last little bit of gas that was in the boat. Still no change. Also this feels to me like it is surging because of an ignition issue due the speed that the surging happens at. It is almost instant.
Does anyone have an idea what direction to go in next? I don't want to just swap parts until it goes away. I may pull the carbs and give them a quick clean, but right now I don't think they are the problem. The unburned oil on the water also makes me think that at least one cylinder is not burning the fuel like it should. Thanks For any help. Carl
It idles like it always has, not silky smooth, but idles. I have to think that the trigger is working since it runs on either upper or lower cylinders. I have checked and gas is getting to both carbs. Plugs are new, and I just ran a can of seafoam through the last little bit of gas that was in the boat. Still no change. Also this feels to me like it is surging because of an ignition issue due the speed that the surging happens at. It is almost instant.
Does anyone have an idea what direction to go in next? I don't want to just swap parts until it goes away. I may pull the carbs and give them a quick clean, but right now I don't think they are the problem. The unburned oil on the water also makes me think that at least one cylinder is not burning the fuel like it should. Thanks For any help. Carl