Gary Woods wrote in
:

If it dies out immediately, there's something blocking the carb...is
this a conventional bowl-type carb? If so, it ought to run for a few
minutes just on that fuel....if the tank and fuel line are OK (pull
the line off the carb and see if fuel runs out), a carb cleaning
and/or overhaul is called for. Often depending on the supplier, and
new carb is cheaper.

Thanks... I followed your suggestion and pulled the fuel line off at the
tank, and fuel was flowing from the tank no problem. Next I unscrewd the
float chamber and it had fuel in it. The float chamber is screwed in place
by some kind of brass, threaded main-jet-like-thing. I blew through the
tiny hole therein, in case it was blocked. I checked that the throttle
cable was adjusted correctly. After that, it fired up first time and runs
with ample power now. I'm not sure what I did that cured it. Perhaps there
was a speck of debris in the main-jet-like-thing in the centre of the float
chamber.

Thanks to everyone for the help!

Al