Petcock question

David Fallon davidinwa at
Fri Apr 25 07:03:04 PDT 2008

Concerning my question about the petcock function on the 750;

I got  another chance to look
at the petcock.  There is a hex on the vacuum tube, so I unscrewed it.
Behind the vacuum tube is a one way valve with a bleeder hole in it.
The bleeder hole was plugged.  Unplugging the hole puts everything back
to working like it should.  The valve was round phenolic disk about 4
mm dia, and 1 mm thick.  The hole was very small; .032 safety wire was
  way too big.   I had to use a piece
of smaller wire to clean it out.  The hole and check valve must be to
allow vacuum to build without releasing between engine strokes as the
vacuum line does come from only one cylinder.  That would prevent the
diaphram and fuel shut off valve from fluttering under low engine
speeds.  The bleed hole allows the fuel shutoff diaphram to close in
about a half a second.

Why don't they include this in the rebuild kit?  Cleaning that hole
required lots of patience and my 4x reading glasses.

Back on the road.  Thanks for all the good responses.

David Fallon

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