dr_bar wrote:I'm going to say it has to do with the rectifier/ regulator. Possibly faulty, it sounds like there is no charge going to the battery and the engine is running off the battery instead of the stator, which would be why the battery drops dead so quick...
The duration of the run seems too short for this to be the case unless the battery has no capacity.
(BTW- the charging system doesn't carry the load when at idle on most bikes - the battery does.)
But a way to double-check it - other than using the correct tool for the job (a voltmeter) - might be to disconnect the headlight so as to reduce the electrical load while running.
On the other hand- I once stored my XT350 with an additional Marvel Mystery Oil in the gasoline.
During the storage period the oil separated and went to the bottom of the tank. At restart time it would only run a short time. There was oil instead of gas in the carb bowl. Draining the bowl fixed the problem. That's probably not the case here but odd things can happen.