err...sorry, did you say you get a 40 second burn before putting them out?
I would suggest invisting in some good ole kevlar wicks. I've only just started on the fire but I can get a good 5 - 8 minutes per burn!
As for putting them out, many people say you should put them out when the flame is only rising 2" above the wicks (they should be a lot higher when first lit and stationary). When you do put them out, dip them immediately back into the kero to prevent any smouldering eating away at your wicks - don't worry the kero won't go up unless it's pretty hot.
hmmmm...all this talk of fire makes me wanna go out and spin - can't wait to get home 
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"The tincture of night began to suffuse the soup of the afternoon. He considered the sentence, and found it good. He liked 'tincture' particularly. Tincture. Tincture. It was a distinguished word, and pleasantly countered by the flatness of 'soup'. The soup of the afternoon. Yes. In which may be found the croutons of teatime."