So went back to basics and changed the spark plug and put more fuel in. Amazingly the 'popping' has now completely stopped.
Problem is now that changing the idle seems to do little, if anything, to the speed of the engine. It's not spluttering or anything. Having said that, due to how rich it was running previously, the oil seems to have a fuel smell and quite watery. Might change that as well to rule further things out.
The engine was running OK prior to the carby clean, and is now back to running OK, so maybe need to fiddle with the settings. Thanks for your reviews so far.
