Ed, I had a HL189 on my WB580 and it was really too small (venturi was less than 1" ) to do the job. The 166B is pretty small with a .625 venturi. If you are hell-bent on sticking with HL, give EC a call at 615-446-6807 and ask for their advice and let them know application, and any modifications done to the engine.
I went with a China copy from Vince at Classic Kart Shop who sells a 1" bore carb. It idles better than the Tilly's and I've had good luck with it so far as have many others. I did have to cannibalize the choke detent spring and slug to use the choke without a cable, but in hindsite, I didn't need the choke at all.
Here is the carb.
Here is the bike/engine I used it on. 580, with modified 820 reeds/cage, intake/stuffer.
With love, Havasu "OldMiniBikes Douche Bag" Dave.