vapor lock, and more

art.robinson art.robinson at
Sun Aug 16 05:31:39 PDT 2009

Déjà vu! I'd all but forgotten starting my '54 AJS Model 20 Springtwin.
It had a choke lever, but the bike wouldn't start if you used it (but it
was a really nice choke lever and perfectly matched the ignition
retard/advance lever on the other bar, which you also never used).

The way you started it was to hold down a small button on top of the
carb, which held down the float and allowed the carb to briefly flood.
The bike would start immediately and run without the choke

When I was a working man I introduced a manufacturing line of
electrically operated stainless steel poppet valves.
They had wide range of applications (and voltages) from aircraft to
commercial coffee makers. 

I wonder if a normally closed valve like this might be a safer
alternative to the vacuum operated gas valve? It could be wired into the
ignition switch and would only open when the ignition was turned on.

A friend of mine used two of them for his washing machine. In those days
the connections were rubber hoses attached to threaded laundry tub
faucets and a flood resulting from a broken hose wasn't covered by your
insurance, as the connections weren't viewed as permanent plumbing. 

The idea worked fine and the problem is essentially the same as ours.

Any thoughts on this idea?

Art in TO

-----Original Message-----
From: gpzlist-bounces at [mailto:gpzlist-bounces at]
On Behalf Of The Masons
Sent: 15 August 2009 20:47
To: William K Denton; gpzlist at
Subject: Re: vapor lock, and more

Like Art--sometimes you get lucky.  This morning I put fresh gas in the
Honda and decided to ride it down to the rental cottage about 4 miles
to cut the lawn.  It doesn't have a choke cable or lever (removed by
previous owner) so I usually just suck some gas into a 5 cc syringe and 
inject it straight into the carbuetor throat.  Its lights on the 2nd
I head up the driveway and make it about 40 meters down the road before
engine died.  I hadn't turned on the petcock.  I know the bike is not
and I'll just kill myself trying to kick start it without the syringe.
is much simpler to push it back the 40 yards and then bump start it on
200 yard sloping driveway.  This bike has no plates. insurance or
While I'm pushing back an Ontario Provincial Police cruiser drives by
slowly.  They really frown upon the locals riding around the roads with 
similar bikes.  He rolled down his window and just said "you're not from

around here are you?"
I rolled it back down the driveway and took the truck over to the other 


----- Original Message ----- 
From: "William K Denton" <wkdenton at>
To: <gpzlist at>
Sent: Friday, August 14, 2009 6:16 PM
Subject: Re: vapor lock, and more

> Jim said, "The manual petcock is only as good as the operator as I
> out this morning."
> ------------------------------------------------------------------
> Jim,
> Agreed.  However, at least with a manual shut-off, you can correct the

> "behavior" [no one to blame but yourself].  With a vacuum shut-off
> you are at the mercy of the rubber supplier's QC and the ravages of
> and fuel reformulation effects on elastomers [everyone to blame but 
> yourself].
> On the brighter side, the OEM petcock packing (4-hole rubber gasket
> 43049-1075) is cheap (<$5.00) and plentiful, as it is used in Vulcans,

> ZX6's, ZX9's ZRX's, GPz's and ZX11's.  At that price, one should just
> "replace every five years" to the scheduled maintenance routine in the

> shop manual.
> Bill Denton
> Yardley, PA
> wkdenton at
> Lazarus Cycleworks, LLC
> Breathing New Life into Old Bikes

More information about the GPZList mailing list