Ah, all our RNs start from cold, even in winter, with full choke and some throttle, as soon as they start the choke is opened (more from habit because with the original choke being side hinged a running engine will pull it closed and promptly choke itself to a stop although with my centre hinged choke that isn't a problem) and I'm off although it is a bit reluctant until I've done about 100 yards. This would suggest you have a weak mixture, my main jets are 70 and compensating 75. The fuel consumption is 35 mpg trundling around town rising to 50 mpg at 50 mph and falling to about 30 mpg on Malcolm Parker's Pennine run. I suggest you check the fuel level for which I use an old lawn mower fuel tank supplying the carburettor on my outside bench with the throttle section removed so you can see the fuel level in the main jet, this is much more difficult on the bronze 22 FZ carburettor.
All three RNs have the vertical coil in the fuel line with no apparent problem Tony.
All three RNs have the vertical coil in the fuel line with no apparent problem Tony.