O.s. 2.10
The big 2-strokes (OS, Moki, others) need larger diameter fuel tubing. It's not just the size of the nipple on the carb. The smaller diameter fuel tubing creates more restriction than the carb fuel draw can overcome. Don't just replace the fuel tubing either. You need larger brass tubing in the fuel tank stopper, larger tubing in the tank, and a large diameter clunk.
I'm running a 24 oz. tank on my Moki 2.10 set up with everything in the fuel system large diameter. I can set the needle where I want and it will hold that setting from full tank to empty (or as close as I care to get). It shows no signs of needing a pump or regulator, either.