I would say it sounds like a "lean" condition. If your timing is correct, I would inspect the accellerator pump for proper function. Best to do it when its cold, so the fumes don't accidentally ignite and give you a new hairdo.
Does it do this at all engine temps? I was thinking that if it only does it when its cold, maybe there is a vacuum leak somewhere in a thermostaticlly controlled device (causing lean mixture).
Hope this helps.
Of course the first paragraph of this is hogwash if it turns out your 280 is injected which I am starting to think it is.
[This message has been edited by Larry Delor (edited 01-11-2000).]