I have a 50hp Mariner 2 stroke 3 cylinder age approx 1990. Iv had a bit of trouble recently the engine runs well upto approx 3/4 throttle and when i push to full throttle it chokes back.The engine is premix and the plugs have some oil on them each time the engine is used.I have had the carbs off and cleaned them also ran the engine and sprayed the carbs with cleaner.Also i noticed that the top carb is feeding a lot more fuel than the bottom one.Is this a matter of just tuning the two carbs together ? Any help would be appreciated. Thank you