Low Idle problem on Nissan Pao (K10 in disguise)

Hi all; afraid I have a low idle problem on my Nissan Pao with it's stock MA10S engine. If I start the car from cold, the auto choke warms the car up at about 1000rpm. Towards the end of warming up, the RPM drops lower and lower until eventually it sits at about 200 RPM or below (sometimes as low as 100 RPM).
I believe the carb on the Pao only has an idle mixture screw; if this is changed it does improve the RPM a little, but it's barely noticable. Until last week the car was undriveable and would continually stall when the RPM dropped too low; I was able to improve this slightly by replacing the fuel filter, HT leads and the coil and was able to drive the car round to my parents house (about a mile) to ask my dad to take a look. The RPM was still hovering around 200-400 RPM and we could find no more adjustment on the carb, so I drove the car home, at which point the car stalled every time I slowed to take a corner and I had to restart the engine (bit of a problem when the car will only start in the "P" position on the automatic transmission).
In our facebook group we have a member in Germany who can rebuild the carb, but I'd like something that I can service and understand it's workings, as it seems the current carb is in need of refurbishment and the parts are incredibly difficult to come by, if not impossible now.
Does anyone know of a weber carb that could be installed instead and anything else required? One member has installed a Nissan Sunny carb, but they've yet to release the details about this.
Any information would be much appreciated.