We're currently experiencing a strange phenomenon with the bike we're trying to get back on the road.

A set of new spark plugs go in. The bike then runs beautifully around the block. Next time we try to run it, the spark plugs seem to be dead. No spark, nothing. Bought another couple to make sure it wasn't a duff batch, same thing happened, bike ran nicely around the block then, dead again.

Anyone ever experienced similar problems or have any clues as to what it might be? Any suggestions would be appreciated.

complete guesses, but how about a lost earth, or a broken coil (or equvilent).

Plugs still clean around the electrodes?

All the bikes I ever owned just HATED any trace of excess oil, unburnt fuel, etc. on the insulator around the centre electrode.

A lost earth sounds like an interesting one. I have had earthing problems on that bike before. The machine has been taken almost completely apart so it could well be a possibility.

Because the bike has been apart, put back together, and cleaned in the process, the electrodes around the plug should be ok but again, it's worth double checking.

Thanks for your suggestions thus far chaps.