50hp Merc 2 stroke dropping cylinder when warm/under load

[Pondskipper]

2000 motor low hours. Owned for 4 years no issues. This year take it out motor fires right up and idles fine. Will run run great through all throttle ranges up to WOT. After about 15 minutes of run time and get some heat in the motor, motor starts to act as if running on 2 of the 3 cylinders. New fuel lines, plugs, fuel filter. Water flowing through cooling discharge hose, not overheating. Before I start swapping parts was looking for direction to head. Acts as though something is breaking down after heating up. Stator? Coil? Trigger? Any help would be greatly appreciated. Thanks

 

[Texasmark]

When it starts doing that stop. Pull the plugs and find the wet one. I assume you have Capacitor Discharge Modules in that engine....self contained...trigger in, high voltage cap to the plug out. If so that makes it easy. Swap that module with another cylinder and leave the plugs as they are. Run again and if it indicates that the problem moved to the new cylinder, your CDM has a thermal problem. They do have such....BTDT

Otherwise pop the cowling and take a battery operated timing light when the engine starts acting up, walk through the cylinders, putting the timing light clip on each sparkplug wire.....maintaining correct direction...imprinted on the clip, and see if one isn't hitting like the rest.

If you pull the plugs and all are the same then maybe your fuel tank vent isn't venting. Building up a vacuum in the tank, engines fuel pump can't totally overcome the vacuum and fuel starvation results.