Years ago I had a 19ft StarCraft bow rider with a 115hp Johnson 2 Stroke outboard. The motor ran great on muffs or in a tub. Take it out on the lake and it would flat out quit or run really badly. I had it into several shops. No one could figure out what was wrong. I was about to sell the boat because I was so frustrated. One day a shade tree mechanic I knew was talking to me and I explained my problem. He came over to the house and in 45 min came in and said it was fixed. He charged me $20. The next day I took it out to the lake, and it ran perfectly. I ran it around all day with no problems. The next day I asked him what he had done. He explained that it was a somewhat common problem on older 2 stroke motors, especially larger displacement ones (I don't know if that is true or not...it is just what he said). It seems that the float bowls in the carbs would get a "skin" built up from using 2 stroke oil. It is (according to him) especially common when the motor is used intermittently or stored for long periods such as over the winter. When the motor was run on muffs or in a tub, the skin stayed in place and did not interfere with the way the motor ran. But when the motor was run out on the lake, the constant bouncing and wave action would make the "skin" move around to the point it would block the fuel from getting up through the carbs. which would of course, stall out the engine. After boat sat for a while the skin would settle back down, and the motor would start and run fine again. Sometimes I could run all day with no problem, but other days I was lucky to be able to run for 20 mins. at a time. After his repair, which consisted of taking the float bowls off the carbs and carefully removing the skin that had built up, I never had another problem. Please understand I am not any kind of expert on this matter, and am just passing along what I was told, and my experience.