This is the carb on my 60X which is the same as yours. The ratchet lever is to tune the mid range mixture with towards the + being rich. The setting is quite sensitive so only go a click at a time if needs be but the centre mark is the factory setting and I've never had to change it. Idle mix is with the air bleed screw on the left and mine is set so the needle covers half the hole in the front. Muffler pressure is pretty much necessary with this carb because it's fairly large.

The 60X is a magnificent engine with its AAC construction. I run mine on zero nitro with 20% all castor. If yours has only had one tank through it then I'd suggest giving it a bit of fairly rich running in for maybe 30 minutes. You'll most likely find there isn't any pinch but this is normal for these engines.