If you want to keep the barrel style carburetor but need one with both high and low adjustments, you need a WYK series carb. The online go-ped parts places have some WYK series carbs available, but they're mostly 13.5mm venturi sized carbs, which I'm not sure but may be too big for your engine. Other WYK series carbs are available but have to be special ordered. You go to Walbro's website and contact someone there about special ordering them.

Cheers,
Charlie