Hello,

First on the fuel, never use any fuel that has Castor in it, actually the maximum allowed Castor in YS engines is 2%, the Castor creates gum on the diaphragm and can clog the internal fuel passages.

Adjusting the regulator, look at it this way, high needle is a regular high needle and the regulator is the low needle.

What I mean by going full power is, once you make an adjustment, do not start the engine at idle and check it right there, instead, start at idle, go full power go back to idle then check.

First set the high needle, unless you are doing dramatic changes on the regulator, (more than a turn) you do not need to reset the high needle at this time.
On the regulator from flush, if it sputters then go cw or closed to reduce fuel to the carb, go 1/8 of a turn a a time or less, after you are rally close go only 1/32 or the thickness or the screw slot at a time, if it slowly accelerates then open it up, don not got 1/4 turn or more, this will only drive you crazy.

Make sure you also have a 1mm opening on the carb at idle when you do this adjustments.

The best fuel I used on the 120 was the wildcat YS 20/20, higher nitro not only gives you more power but it improves the idle a lot. If you can't find Wildcat, then go with fully synthetic helicopter fuel, like Cool Power, Helicopter fuel has more oil in it, and the YS 120 should run on 20% oil.

Which glowplug are you running? and what prop? I used 15x10 APC with excellent results, you can also use APC 16x8

Regards