1993 Yamaha 40 two stroke. running issue

[Empennage]

Hi everyone,

I have a 40 horse Yamaha 2 stroke that was stored for 18 years, cleaned the carbs, new fuel line, plugs, fuel tank. Engine starts and runs great for 10 minutes or so then only runs at 2000 rpms at full throttle. the rest of the time. Its almost as if its only running on one cylinder

Any help would be appreciated!

Thanks