That sounds as if you hadn't got all the crud out of somewhere in the carburetors, Mark: the main jet and the emulsifier would be the chief suspects.
It is sometimes quicker and more certain to replace parts than to recondition them. When I was a lad I used to buy second-hand Lucas point sets from wreckers to keep my succession of old cars running. Half the time they didn't fit the car properly and I had to modify them. Fortunately simple parts like that come from China now and cost almost nothing. They are incomparably better parts than the Lucas ones, too. The world improves itself, albeit gradually.
In my experience there are just a few slightly tricky aspects of working on the Keihin or Ruixing carburetors.
First, there is getting the emulsifier out without damaging it, because in some cases it is held in by gum. I only see this in a minority of cases, and so far if I use enough carb cleaner, and blast it into the right places, it is handled fairly easily (especially compared with some other carburetors, which are really difficult to take apart, or can't be taken apart). Of course you then need to get the emulsifier, and the main jet, really clean. This is where most people fail: you don't just need there to be a hole in each place, it needs to be cleaned until it is the same size as a new one. I use the right sized jet drill, pushed in backwards so it doesn't enlarge the hole. If it won't go in easily, apply more carb cleaner.
The next issues are the previous tenant's sometimes brutal treatment of the idle mixture screw and the plastic idle jet. Both problems are best cured by simply replacing the damaged parts so you are putting it right once and for all.
Aside from that, the big seal that goes around the top of the float bowl is a pretty delicate object. It is usually undamaged, but it will be hard and brittle, so either leave it in place or replace it with a new one.
The only other bit that has a reputation for needing occasional replacement is the float needle. I've never had to replace one, but I may have been lucky.
