For it to suddenly die like that, it would have to be fuel and most likely a blockage.
I had similar problems with a Super Tigre G.51 once and ended fixing the problem by removing the carby, stripping it and soaking the component pieces in Methylated Spirits (which is a cousin of methanol) I also probed the fuel nipple with some fuse wire.
That cup of meths turned yellow from the congealed "gunk" in the carby (not to mention the micro insects that had been sucked in and had died in there.) The engine ran fine after I put the carby back together.
But your problem could also be something floating around in the tank.
Is there anything resembling bits of cottonwool in it? (Caused by nitro going "off" from moisture absorbtion) This stuff turns up from time to time and will eventually get sucked into clunk and the block the fuel lines.
It may be worth removing the tank, opening it up an flushing it right out with some meths, which will also remove any moisture etc in the system.