Necessity of Turning Off Fuel Cock?

 What is the purpose of turning off the fuel cock when the engine is not
running?  My owner's manual gives this instruction, which I'm trying to
follow unless the bike is off for just a few minutes.  I'm just
wondering why.

 meyerdt@yahoo.com wrote:

The need to do that all the time is quite overrated, unless your carburetor
fuel float(s) aren't working properly.

The idea is that, after a time, fuel will evaporate from the carburetor(s)
and leave a coating of varnish on all the little parts that need to stay
clean.  So long as fuel is actually flowing through the carbs, it keeps the
varnish washed away, but when the bike is not running, that varnish (the
stuff in gasoline that doesn't evaporate) builds up as the fuel evaporates
there.

So shutting off the petcock limits the amount of fuel that can evaporate
from the carbs.  If you routinely ride several times a week, for example,
there's no need to shut it off under normal conditions (i.e., your carbs are
working right).   If you're gonna store the bike for a good part of the
year, be sure you remember to do it then.

 meyerdt wrote this on Sun, 11 Jun 2006 12:40:45 -0700.  My reply is
below.


It's a failsafe backup against the (remote) possibility of a
carburetor float valve's sticking open.  You could get very unlucky if
that carburetor were over a cylinder sitting with its intake valve
open.  The cylinder could fill with gas.  The next time you tried to
start the engine, it would make only a partial rotation before closing
the intake valve and compressing the fluid.  This is hydrolock.  If
(one of) the other cylinders with a full charge is pushing against it,
something will give ~ maybe a connecting rod.

This is not a problem on vehicles with carburetors located above their
fuel tanks.  Other vehicles, such as farm tractors, have a
fuel-line/oil-pressure interlock to backup the fuel cock that
backs up the carburetor floats.

If you've inadvertently left the fuel cock open, put the bike in a
middle gear, engage the clutch, and push the bike a little to turn the
engine over.  If you can't turn the engine, better take out the spark
plugs, hit the kill switch, extinguish other nearby sources of
ignition, and try again.

--
.. Chuck Rhode, Sheboygan, WI, USA
.. 1979 Honda Goldwing GL1000 (Geraldine)
.. 1978 Honda Goldwing GL1000 (Fenris)
.. 59F. Wind NE 8 mph. Clear.

 

Another reason why they have those "off" positions:  on some
rare occasions one wants to remove the tank from the bike.
With the fuel in it.  

Jim


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 meyerdt@yahoo.com wrote:

there's a snappy response in there but I'm not the man to give it.  ;-)