Storage, preventing old gas from messing up carbs?

When not using the bike (z650 B1) for a few weeks some one told me a good idea was to put the fuel tank to ‘OFF’ and let the motor run until it runs out of gas. (The theory being that less fuel in the carbs wold be a good thing as it can clogg up over time. )

Is this true?

(My search attempts on the topic failed, probably due to lack of correct description, sorry). 

Although there is still some controversy surrounding the subject, I am convinced that after three or four weeks, gasoline, especially E10, begins to dry up and turn into a varnish-like substance.
The method you suggest will remove only that fuel that can be picked up by the jets, leaving a puddle at the bottom of the bowl. I think a better approach is to drain the carbs via the drain screws.
The best method is to ride the bike regularly.

I turn my petcock to OFF every time I park my 1977 KZ650.  If I'm putting the bike away I shut off the petcock a couple blocks from my house so the fuel level will be somewhat low when I get home.  I start my bike once per week even in the winter and let it run for 10 - 15 minutes; that way the battery stays charged, oil remains on the cylinder walls, and I know for sure the bike will start right up when spring comes.  If you plan to let the bike sit for an extended period I would suggest draining the fuel bowls so varnish doesn't occur.  Many years ago I let my bike sit all winter with fuel in the carbs and when I started it in the spring varnish had clogged things up rather badly which required a thorough carb cleaning to fix.   That will not happen again.  Also, turn the petcock to OFF every time you park the bike!  Ed

I fill the bikes with non ethanol gas in the winter and start them at least once per month when not riding regularly. I've been bitten by the glowing, green gas so I am extremely careful with my vehicle fuel.  
 

Looks like you have collect some water bubbles in the fuel bowl.

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I fill the bikes with non ethanol gas in the winter and start them at least once per month when not riding regularly. I've been bitten by the glowing, green gas so I am extremely careful with my vehicle fuel.  

 

Never seen that, what causes it?

I try to start and ride my bikes every two weeks, never more than three. Our winters in Richmond, VA are not to bad, so that helps. After 15 years of doing this, I have never had to clean  carburetors on any of my bikes.
I do pick up a few bikes cheap each spring, from people who let there bikes sit over the winter and can't get them to start or run properly do to gunked up carbs.

If you want to drain the bowls for real, you will have to drain them from the bowl drains.  The bike is not able to literally "run on fumes" like people often say.  Once the fuel level drops below the opening of the pilot jet, the bike will stall, but there will still be a bit of gas in the bowls.  Plus, using the bowl drains gets rid of some non-dissolvable debris that collects at the bottom of the bowls.

I try to drain the bowls if I know I won't ride it for a few weeks, and especially before winter.

I use "marine" version Stabil in the gas year around.  I live in So Calif so the bike can be ridden year round but because traffic is so crazy here sometimes the bike sits for a month or three because I don't feel like risking my life.  Anyway, the fuel stabilizer keeps the fuel from coagulating and plugging up the carbs.  Highly recommended and it doesn't require careful draining of the carbs and what have you.

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... because traffic is so crazy year sometimes the bike sits for a month or three because I don't feel like risking my life. ...


 

I know the feeling.  Last year was particularly bad.  With less traffic everybody was driving like it was a go kart track.  I drove by more overturned cars and cars fully enveloped in flames last year than probably the previous 20 years combined...not to mention so many semi's laying on their sides with cargo spilled everywhere.  

Thank you everyone!!!

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Plus, using the bowl drains gets rid of some non-dissolvable debris that collects at the bottom of the bowls.

That's very true.  I always find crud at the bottom of the bowl when I take them off.

Here is one more reason to occasionally remove the drain screws.  At least for the VM carbs, if you wait too long the screws can get stuck.  Like really stuck.  I've stripped the heads on a few, and one time broke the head off the drain screw and then broke the float bowl trying to get the piece out.