Why oh why, when you leave a vehicle that ran, does it then refuse to start a few weeks later?
Couldn't blame Mike, for although he has now permanently soldered together all the temporary dash connections, the spark at the plugs was very good, which means he didn't mess up the wiring. Must be a fuel problem then.
Took the top horn off the carb, and found that the accelerator jets weren't working. Took the fuel pipe off, checked the fuel flow, all ok. Took the top off the carb, which was full of fuel as it should be. Removed and checked shut off valve. Found ok. Put the top back on the carb, try again, and it still won't start. The fan drive belt then decided to snap for good measure. Not turning out to be a good day.
Several taking-apart-and-putting back-togethers and much head scratching later, it still wouldn't start, despite removing and cleaning/checking every component I could. Decided to put the top back on the carb, and address why the rubber drive coupling was rubbing on its guard.
While re-shimming the gearbox height to solve the rubbing problem, my trouser pocket got caught on the carb, and the accelerator jets were suddenly working! Powered up, and engine then started first time. WHY DIDN"T IT DO THAT TO START WITH!?! AAAAARRRRGGHHH!