We tuned a DZ a few weeks ago that did the same thing. Poor lower range, idle and died. We wound up with the regulator about 2 to 2.5 in from flush. Then the motor ran perfectly with typical YS response and a fine idle. Each motor takes a little bit different setting. I have seen from 2.5 turns in from flush (rich) to .5 turn out from flush.

Coolpwer 30%, OS F or YS 4 plug are the standards we are using.

Mark