Carb needed

[MGR]

I have a Tillotson HR71A carb on my Nipper (1835cc VW engine) , but am having a lot of problems (problems starting, misfires, rough running etc), which my mechanic believes are due to the carb. Thus I am looking for a replacement.
Anyone got something suitable that I could buy or even better borrow then buy if it fixes the problem.
Thanks a lot.
Malcolm Read
G-BRIK
PS The Tillotson works inverted but I am just looking for any carb that is know to work OK on that engine. The PPS Tillotson is also quite small so I may need to modify the top cowl to get a different carb to fit.