Webber carb? Rust? not sure

This has probably been covered before so please bare with me. I have a 91 reg clipper which i have owned for the last 17 months…its a daily runner.  When i first bought it, it had problems with revs when idling, so i had a weber carb and manual choke fitted by crazyquiffs, the problem was instantly solved (till now maybe).

A couple of days ago it started spluttering and running roughly which only seems to be solved by flooring the acclerator, which is obviously not ideal, or by pulling the choke out.  The problem can come and go during a journey so is obviously not affected by temperature.

Any ideas on how to check what the problem is would be greatly appreciated…

Cheers Columbo