With cdi you can pretty much lean it down to one turn or slightly less, at least on mine with Coolpower 30% heli with 23% oil after break in.

There is nothing wrong with the stock YS plug. Although, it doesn't last as long as the after market one like NGK ME-8 or the Rimfire VR-2. The YS one will start misfiring after about 30 flights sometime, the key is to file the tip of the electrode to a slightly pointed shape when new, check the gap & clean the tip on a regular bases.

I have tried all three brands on both 170 & 175 cdi & prefer the Rimfire, it's the most consistent by far.

Hope this helps,

Adrian