I just cleaned and installed my first Gurtner on a 77 "Cane" once it's warmed up a bit it idles fine, does not leak and runs perfectly.
I tend to think you should het it running well as a stock ped before you start trying to change things.
If you can find a good deal on a NOS carb it can save you alot of greif.
Remove the petcock and see of the screen is clogged.
Rusty