The YS is much different than other motors because of the pressurized system. On the older YS's 4 and 2 strokes, the regulator was the low end. On the newer YS starting with the generation 2 53 4s, a low end needle was added which negated the adjusting of the reg for the most part.
As chuck stated, start with the reg flush with the engine and you should not have to turn it in more than 1/4 turn. The regulator primarily affects the midrange of which the low end relies upon. The top end is independent.
The key to a sweet YS is the tank setup. Make it as simple as possible with NO air leaks. It will let you know in a heartbeat if there's a leak. Believe in the motor when it tells you that....