I used a very rich run in period on my 50sx also! I started with the needle set almost 3 and 1/2 turns out and slowly wound it in. I ran 2 8Oz tanks (at 3 and 1/2 turns out) through the engine, then after each subsequent tank full I would wind the needle in 1/8 of a turn. Use various rpm settings also and try not to hold any given rpm for too long. Also allow the engine to cool fully between tanks. Yes there is not problem "that I know of" in storing a half run in engine for a while as long as you use after run oil.