vapor lock, and more

John Soliday johnsoliday at
Wed Aug 12 16:57:39 PDT 2009

I think part of the reason the manufacturers went to the vacuum petcock was
for those of us who couldn't remember to shut it from "on" to "off", thus
avoiding the potential "Exxon-Valdez refined spill" in one's garage!
Obviously a vacuum petcock costs a tad more than a simple on-off variety so
I think there must have been a reason they did it.  All of this talk
concern's me a bit as mine still only has now 4K miles on it but symptoms of
the dreaded leaking petcock...


-----Original Message-----
From: gpzlist-bounces at [mailto:gpzlist-bounces at] On
Behalf Of chris marquis
Sent: Wednesday, August 12, 2009 11:18 AM
To: gpz
Subject: Re: vapor lock, and more

I to ,even after growing up racing dirt bikes and 3 wheelers (remember
those) sometimes forget to turn the gas on!!Did it on my gpz a couple times
once right in front of a police car,i figured sure as hell this was going to
get me at least a 20 minute lectuer and or a ticket,you don`t want to get
thier attn. around here the only help you get is the prior mentioned
things.  lol  They used to have little stickers at the motorcycle dealer in
town that said (turn the gas on dummy) that we used to put on top of the
tank,  lol that did really help , but my point is that i just don`t trust
the automatic petcocks i`ve had/seen to many problems like this one,going
over some railroad tracks and the bike quit ,at night of course so it took
half an hour to see that the vacume line had come loose and shut the fuel
off on  me !! in the bad part of town of course  !!! Riding not just alot of
fun-but an adventure!!!!!!!!!!!!!!!!
best of luck  guys   Chris

--- On Wed, 8/12/09, mrgilmore at <mrgilmore at> wrote:

From: mrgilmore at <mrgilmore at>
Subject: Re: vapor lock, and more
To: art.robinson at, gpzlist at
Date: Wednesday, August 12, 2009, 10:25 AM

Art!? Guys,

Listen to Pete S.? and now me - please!

I took a motorcycling camping trip back in 2000 and went around the four
corners of California on my GPz - almost...

To make a long story shorter, it was a blast doing the solo trip with my
Ventura bike pack gear, tent/sleeping bag, mini-kitchen, etc.? until the
petcock thing reared its ugly head.

At the time, I had no experience with any such thing and had no clue as to
why it wouldn't run, and once I found the gas all?around the vicinity of the
petcock and?in the oil, I went to a local shop, drained it, refreshed it,
and kept going.? That is until it happened the next day, and the next...?
Ultimately my trip ended with my needing to replace the water pump, and the
location I was in had no such item on a Sunday, so I had to get rescued by
my girlfriend who drove up to Watsonville in my empty van with ramp and that
was that.? I surmise that the watered down oil contributed to the demise of
my water pump.? I was incredibly lucky to not have any other significant
internal damage to my engine, but then again, I did have to change out that
original engine due to the #3 cylinder losing its compression....

Get the petcock changed and get the filter too.? You'll be better off for it
whether you take the long haul or just tool around town.

Believe that.

Ron Jordan

Altadena, CA high miler on engine #3 and still loving this heavy, yet fun

-----Original Message-----
From: art.robinson <art.robinson at>
To: 'gpz' <gpzlist at>
Sent: Wed, Aug 12, 2009 5:46 am
Subject: RE: vapor lock, and more

I agree with the simplicity of adding a manual petcock and reading all
the problems with flooded cylinders, locked engines diluted oil and bent
con rods, I become nervous just thinking about it.

On the other hand when just a lad with my brand new '62 Triumph
Bonneville, I forgot to turn on the petcocks (there were 2, each feeding
a separate carb) and I managed to make it from my mother's house down
the street to the main road. 

Just about to make a right turn in front of a f*#!king big speeding
double-decker bus and the bike sputtered and my guardian angle tapped me
on the shoulder and said, "Arsehole (remember we're in England) you
didn't turn on the petrol!". I grabbed the front brake and the nose dove
right down as the bus passed inches from my front wheel.

Two more drops of gas available in the carbs and I would have made a
great impression on the front of that bus and would never had the joy of
riding a GPZ or anything else for that matter!

My heart sped up just recalling the incident!

Now, 47 years later with my memory in tatters, I'm just too scared to
fit a manual petcock, so I'll just keep fretting and sniffing around the
bike and hope for the best.

Art in TO

-----Original Message-----
From: gpzlist-bounces at [mailto:gpzlist-bounces at]
On Behalf Of chris marquis
Sent: 11 August 2009 08:27
To: gpz
Subject: Re: vapor lock, and more

This kinda stuff is the reason i ALWAYS spend 3-4 dollars for a manual
shut off and put in the line (with a filter ) cheapest insurance i know
against a whole lot of problems!!!!!!!!!!!?? Chris

--- On Tue, 8/11/09, Drew Blanchard <drewblanchard at> wrote:

From: Drew Blanchard <drewblanchard at>
Subject: Re: vapor lock, and more
To: "Bob Nelson" <majordad at>
Cc: "GPZ LIST" <gpzlist at>
Date: Tuesday, August 11, 2009, 7:54 AM

Ah, well, this is not what I expected to hear.? And I DID just have the
carbs cleaned and adjusted by my local Kawi dealer (picked up some
before I installed the fuel filter, an
d also needed the pilot jets
adjusted).? So, this points to a bigger issue?? The petcock has NOT been
"prime" position.? I've noticed a whiff of gas around the bike for a
but it was faint, so I put it on the back burner.

When I pulled the tank, the petcock continued to dribble.? Ultimately, I
to prop it on its side and lean it againt the wall (the tank is less
1/2 full) before I could walk away and work on the bike.? This lends
credence to hydrostatic lock; the cylinders, especially 2 and 3, has
fuel in them.? At the time, I was focused on vapor lock,? and worrying
geting home before my dogs exploded from a loooong day.? It never
to me there shouldn't be so much gas in the cylinders.? Now I need to
out how to get the back to the dealer's.

Grrrr.... (again)

Thanks for the input, Bob!

Drew in VT

On Tue, Aug 11, 2009 at 4:05 AM, Bob Nelson
<majordad at>wrote:

> Drew, first things first, if the motor wouldn't turn over and you had
> squirt out of one or more cylinders after you pulled the plugs, it was
> hydrostatic lock, not vapor lock.? Hopefully you only had one flooded
> cylinder.? There are two requirements for this to happen.? First, you
had to
> have gas flow out of your petcock without vacuum applied to the
petcock? (or
> the petcock is in the Prime position, if that is the case switch the
> to the normal or run position).? The second requirement is a
> float valve in the cylinder involved allowing gas to over fill the
carb and
> drain straight into the cylinder.
> If you are lucky the flooded cylinder was one of the outside carbs.? I
> lucky because I am pretty sure you can pull the float bowls without
> the carb rack out of the engine.? If so, you can make sure that the
float is
> free to move and not stuck open.? If it is free to move, then after
> the float bowl back on, I would tap the float bowl repeatedly as I put
> petcock in prime to try to help the float overc
ome any stiction and
> hopefully float and thereby close the float valve.? If the float is
> open, you will need to disassemble, clean and carefully watch the
> couple of times you start the bike to make sure your cylinder doesn't
> again.? If you are unlucky, bad things can happen after hydrostatic
>? You could end up with bent valves.
> Anyway, if this occurred out of the blue and not immediately following
> carb cleaning and reassembly, you might have fallen victim to what I
> suspected happened to me.? This March I rode from Charlotte to Florida
> some friends after not having any problems for a very long time.? The
> morning I had a cylinder locked.? I attributed it to contamination
> running way down into the reserve on my fuel tank and running some
> through that partially blocked the float valve open.? After I cleared
> cylinder and rode that day, the problem didn't recur.
> As far as follow on leaking not associated with the locked cylinder,
> would have to come from a leaking hose or the fuel tubes that connect
> carbs.? Hopefully you will just find that your fuel line is cracked
> that would be the easiest repair.? But that also points to a bad
> since you should not have fuel flow through the petcock when there is
> vacuum present to the petcock unless it is in the Prime position.
> Hopefully this rambling makes sense to you and helps.? Good luck!
> Bob
> Drew Blanchard wrote:
>> After a chilly start to the day, temps went into the upper 80s.?
>> forward to my ride home, I thumbed the starter and was rewarded with
>> very
>> brief "thump" and some starter whine, but that was it.? Motor didn't
>> over, and the starter seemed to be trying to move an immovable
>> Fearing the worst but knowing everything had been fine on the ride
>> work, I pulled the tank and plugs to see if the motor would move
>> compression.? Yup.
>> Note to self, remember to stuff rages very tightly over
the spark
>> openings.? Messy.? Very messy.
>> When reassembled (and what a bitch it was reconnecting the fuel line)
>> motor initially made the same noise, then turned over with ease.
>>? Obviously
>> it was vapor locked.? I never had this issue on my '95, but that was
>> a
>> stock set up.? Anyone else have this issue?? Is there a preventative
>> measure
>> I can take?
>> Didn't get to ride the bike home, because somewhere, somehow I have a
>> nasty
>> fuel leak.? If I didn't know better, I'd say the leak was coming from
>> bottom of the motor.? And landing directly on the exhaust pipe.? I
>> very
>> fortunate the motor never actually started.? Every time I turn the
>> over I get a nice, steady drip, and I can't see where it's coming
>>? I'd
>> worked on the bike for several hours in the heat, and quit for the
>> Fortunately, our maintenance guys at school let me put the bike in
>> garage for the night.? Once on the center stand, no leak.? Moving the
>> or leaving on the side stand = leak.
>> Grrr.....
>> Drew in VT

Drew Blanchard
Technology Teacher
Winooski City Schools
Normand St.
Winooski, VT 05404
(802) 655 - 3530 x6073

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