G'day I have some eight Saitos and they all take a while to run in before you can get a stable low idle and good transition. I generally run them in according to the instructions then after three of four tanks, I fly them but with the high setting quite rich (at least half a turn and more). I then keep flying them until I notice that they will idle and transition better and at that stage I make small (1/8) turn adjustments to the low speed needle for a better idle and transition and then fly again. By the time they have run for about an hour, they are beginning to settle in. My 72 spent its first couple of flights in a Four Star 60 just plodding around blowing lots of smoke and not idling very well but it has since moved to a Kadet Senior and at first it would not idle slowly to allow me to land so I used to just kill the engine and float in. Now, about an hour later, I have adjusted the low needle and it just putters at a very low stable idle for nice easy landings and its transition

The moral of the story is to resist making lots of adjustments before it gets a chance to run in a bit. And don't expect full performance from a new engine. You won't get best throttle response until the engine has had at least an hour's running. I just put up with poor idle initially but it soon comes good. I use commercial 10% nitro fuel with 15% synthetic and 5 % castor. I had to strip an engine after a bad prang recently and was expecting to find some coke from the castor but the inside of the engine after about 2 hours running was completely clean.

The exhaust gas from a four stroke is hotter than a two stroke and as a result four stroke mufflers get pretty hot. Also, your engine will cool better in the air than sitting on the ground.