Re: Trying a new carb!
When you mention the choke lock I'm thinking you maybe got the 14mm Dellorto SHA copies? If so the choke should also unlock if you quickly crack the throttle open fully.
On a stock 2 port PK80 I'd say the 14mm SHA would be about right although with the stock intake it might not as the intake's ID is pretty small in comparison to the carb's bore...that alone might make it a bear to get jetted right. Add a nice manifold with an ID that matches the carb, a decent tuned pipe on the other end a tight squish setting and I bet you'd see some nice gains and actually have a power band that you can feel. If you have access to a small torch or even a welding rig of some kind I'd seriously consider fab'ing up a manifold for your experiment.
I have a Chinese Walbro copy that I bought from Tsunami Bike in Hamilton, not sure of the model# Walbro it copies but it's about a 15mm bore. I've not used it yet but I'm thinking it's going to find a home this winter on my Riff Raff build.