I have been flying YS engines for most of my RC experience. I have recently been flying them in a race setting in warbird racing. Early on in my RC experience, "tuning" was an issue. Not the engine but my knowledge. Now that I race these, I have learned its not just tuning. You need to know how to let the pressure build up and not go wide open so quickly while setting the needle. Once the routine is set, there is no better four stroke for power. I run 60% nitro and that in itself creates the possibility for tuning issues, but I have none. When I race these, I do around 1-2 practice flights, then 4-5 race flights. Thats 5-7 flights. Probably more than you fly your "sport" plane in a day. These are reliable, durable and poweful. What more could you want? As far as the gaskets or seals going, most people run after oil in these and the silicone gaskets are ruined. Again these need a different set of protocols. Many use a non petroleum oil for after run. I just use 100% synthetic oil.
I have 3 race planes currently, a 70, a 110 and a 115. All three start the same, tune the same and perform the same. Its a proccess- learn it and enjoy the strongest 4 strokes out there.