Keeping Manual Fuel Petcock On Good Advice?

[High Plains Thumper]

I found this posted on a Suzuki LS650 Savage forum. This regards
replacing the OEM vacuum operated petcock with a manual petcock from a
Yamaha Raptor 660 ATV. Is this sound advice?

[quote]
To give you a numerical quantification on leakers, there has only been
two leaking float valve assemblies ever noted after changing over to a
Raptor, both of which had been leaking on those particular carburetors
since before the stock petcock was removed. In both cases the user
dropped the bowl and changed out the damaged float valve assembly. In
both cases, it was a simple mechanical problem with the carburetor that
was due to previous abuse. In neither case did any gasoline get into
the sump.

Remember, gasoline in the sump has NEVER YET HAPPENED due to a Raptor
petcock conversion, indeed the only gas in sump episodes of any severity
(such as could possibly result in a fire, etc.) have happened with the
stock vacuum actuated petcock diaphragm failing and running gas down the
vac line.

But we are all watching diligently for that first Raptor gas in sump
episode as logically it is a possibility, abet a slim one.

Fact is, you leave your Raptor on -- nothing bad happens. Some of us
(Serowbot, Oldfeller) leave our Raptors on all the time as a matter of
habit, only shutting it off for any long term storage periods. Raptors
don't cause any known failure modes that have any identifiable frequency
even when left on.

Vac petcocks however WILL FAIL INSIDE THEMSELVES DUE TO RUBBER AGEING on
a almost certainty basis over a 5-15 year period. Vac petcocks as a
separate system have 5 known failure modes and ARE KNOWN to put gasoline
down into the sump with some of them.

When using normal pump gasolines (not fancy nitro racing fuel) no Raptor
petcock has ever failed in 20 years and 100s of thousands of
installations on both RVs and Savages. They just work.

And if your float valve assembly isn't in sorry shape to begin with,
Raptors do work flawlessly in the Savage motorcycle.
[/quote]

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1340099972

--
HPT
George Hostler
1987 Suzuki LS650 Savage
1971 Honda CB100

[Tim M.]

I'm not sure I understand. It sounds like they are recommending
replacing a vacuum-operated petcock with a manually operated one
because (diaphragm in) the vacuum-operated petcock can fail, leaving
the petcock in the "open" position, so that the carb float bowl's
check valve is only thing preventing fuel from flowing to the intake
tract of the cylinder head. But then they recommend leaving the
maual petcock in the "open" or "on" position, so that the carb float
bowl's check valve is only thing preventing fuel from flowing to the
intake tract of the cylinder head.

This sounds counterintuitive to me.

[High Plains Thumper]

Tim M. wrote:

> I'm not sure I understand. It sounds like they are recommending
> replacing a vacuum-operated petcock with a manually operated one
> because (diaphragm in) the vacuum-operated petcock can fail, leaving
> the petcock in the "open" position, so that the carb float bowl's
> check valve is only thing preventing fuel from flowing to the intake
> tract of the cylinder head. But then they recommend leaving the
> maual petcock in the "open" or "on" position, so that the carb
> float bowl's check valve is only thing preventing fuel from flowing
> to the intake tract of the cylinder head.
>
> This sounds counterintuitive to me.

Oh, you got me thinking. Actually, I think what the individual is
attempting to state is that the Suzuki carburetor bowl needle valve
assembly is so reliable, that it can be totally depended upon.

It will never fail and therefore, the petcock can be always left in the
ON position.

The only way an OEM vacuum operated petcock can put fuel down the carb's
throat is leakage through a failed vacuum diaphragm, allowing fuel to
flow down the vacuum line.

Then why do OEM's put a vacuum operated petcock that automatically shuts
off the fuel when the engine is not operating?

[David T. Ashley]

On Fri, 13 Jul 2012 08:44:52 -0700 (PDT), "Tim M."
<krustykritte...@gmail.com> wrote:

>I'm not sure I understand. It sounds like they are recommending
>replacing a vacuum-operated petcock with a manually operated one
>because (diaphragm in) the vacuum-operated petcock can fail, leaving
>the petcock in the "open" position, so that the carb float bowl's
>check valve is only thing preventing fuel from flowing to the intake
>tract of the cylinder head. But then they recommend leaving the
>maual petcock in the "open" or "on" position, so that the carb float
>bowl's check valve is only thing preventing fuel from flowing to the
>intake tract of the cylinder head.
>
>This sounds counterintuitive to me.

Modifying a system in such a way as to claim it is more reliable but
so that a single-point mode of failure still exists is a pretty common
defective way of thinking. (Of course, modifying it so that the SAME
single-point mode of failure still exists is less common.)

I've got a idea.

I'm designing an airplane. It will have three independent hydraulic
systems, and they couldn't all fail.

That sounds very safe.

But I'll route these systems together at certain points so that a
failure unrelated to the hydraulics can cause all three hydraulic
systems to fail.

http://en.wikipedia.org/wiki/United_Airlines_Flight_232

DTA

[High Plains Thumper]

David T. Ashley wrote:

> Modifying a system in such a way as to claim it is more reliable but
> so that a single-point mode of failure still exists is a pretty
> common defective way of thinking. (Of course, modifying it so that
> the SAME single-point mode of failure still exists is less common.)
>
> I've got a idea.
>
> I'm designing an airplane. It will have three independent hydraulic
> systems, and they couldn't all fail.
>
> That sounds very safe.
>
> But I'll route these systems together at certain points so that a
> failure unrelated to the hydraulics can cause all three hydraulic
> systems to fail.
>
> http://en.wikipedia.org/wiki/United_Airlines_Flight_232

Bad advice to newbies abounds on the Internet. I thought it was common
sound advice by OEM's and MSF to shut the fuel petcock when the bike was
parked. This was to prevent fuel from continuously draining since
carburetor is gravity fed, if there ever was a failure of the carburetor
float needle valve.

Otherwise one could encounter fuel inside the engine's combustion
chamber, causing hydraulic lock if start was attempted, possibly
damaging the engine (fuel is incompressible). Also, fuel could seep past
the piston rings into the crankcase, diluting the oil and overfilling
the crankcase.

[The Older Gentleman]

High Plains Thumper <h...@invalid.invalid> wrote:

> Oh, you got me thinking. Actually, I think what the individual is
> attempting to state is that the Suzuki carburetor bowl needle valve
> assembly is so reliable, that it can be totally depended upon.
>
> It will never fail and therefore, the petcock can be always left in the
> ON position.

I wouldn't believe that. If you can turn off the fuel, do so. Always.
Quite apart from anything else, if a hose starts leaking between tap and
carb, it won't matter a damn that the float valve is sealing.


--
Triumph Street Triple Yamaha XT660 Tenere Honda CB400F
Suzuki TS250 x2 GN250
chateaudotmurrayatidnetdotcom Nothing is more dangerous than an
idiot with a set of cheap tools and a dad "who had a bike once"

[High Plains Thumper]

The Older Gentleman wrote:

> High Plains Thumper wrote:
>
>> Oh, you got me thinking. Actually, I think what the individual is
>> attempting to state is that the Suzuki carburetor bowl needle valve
>> assembly is so reliable, that it can be totally depended upon.
>>
>> It will never fail and therefore, the petcock can be always left
>> in the ON position.
>
> I wouldn't believe that. If you can turn off the fuel, do so. Always.
> Quite apart from anything else, if a hose starts leaking between tap
> and carb, it won't matter a damn that the float valve is sealing.

Well, really what happened was a thread within the technical documents,
which according to the so-called rules of conduct were not supposed to
be posted to the technical documents section. Individuals stated they
always kept their Raptor manual petcocks on without any problem. I
replied that this was not wise advice for reasons stated.

Then I got a posting violation warning E-mail. All those messages were
deleted along with mine and replaced with this one by the moderator.

Only a week ago I received an invitation E-mail from them, because I
hadn't posted there since 2004. It was just time for me to move on.

I thought the replaced advice about petcock reliability and to leave it
on was very poor at best. I deactivated my forum membership.

[Vito]

"High Plains Thumper" <h...@invalid.invalid> wrote

| Then why do OEM's put a vacuum operated petcock that automatically shuts
| off the fuel when the engine is not operating?
|

Same reason you were not allowed to buy a Suzi Gamma like Canadians/others
could: Because we have a DOT that makes rules for our safety <grin>.

I lived in Sandy Yago during the Jimmy Otter gas crisis. There was an
English news station across the border advertising unleaded regular foy 40
cents/gallon when we were paying $1.20. Asked why the Mexican minister
said "Because the US has a DOE and Mexico does not."

[High Plains Thumper]

Vito wrote:
> High Plains Thumper wrote

19 years ago, I ruined my recently overhauled SL125 motor on my 1971
CB100 when I traveled up an 8 mile 4% grade outside Sandy Yago. Then I
froze myself with a light jacket traveling back when night fell during a
November. I have a degree from the DOE.

With my mustache, I've been mistaken for being from the other side of
the border.

Does this mean I should drink the $1.20 kool aid instead of the $0.40?

[Mark Olson]

High Plains Thumper wrote:

> I thought the replaced advice about petcock reliability and to leave it
> on was very poor at best. I deactivated my forum membership.

Exactly. If you have a manual petcock, turn it off when parking.

If you have a vacuum petcock and you're worried about the rubber
bits inside deteriorating, take it apart and look at it. Kits to
replace all the rubber bits aren't all that expensive. It's something
you _might_ have to replace every 15 years or so.

[High Plains Thumper]

That's what I thought. I replaced mine in 2003, which is 16 years later
(1987 model year), thus validating your observation.

Replacing the OEM vacuum petcock with a manual one that has a smaller
profile to allow removal of the tank without removing the petcock
first has merit. However, the caveat to the Raptor is the reserve is
smaller, giving one a 20 mile reserve instead of 30 mile, unless one
modifies the main feed tube height.

Living in these rural parts, I don't like to be stuck so I purchased a 1
gallon (actually 0.9) Reda Portable Motorcycle Gas Can, fits in a
saddlebag. But I don't always use it, so its nice to have a better
chance to find a gas up within reserve range.

Also, I don't remove the tank that often, so defueling is somewhat a
pain, but I can manage.

[The Older Gentleman]

High Plains Thumper <h...@invalid.invalid> wrote:

> Then I got a posting violation warning E-mail. All those messages were
> deleted along with mine and replaced with this one by the moderator.

Jesus. How pathetic. Sounds like Krusty banning anyone who disagrees
with his technical crap.....

You were right to move on.

[High Plains Thumper]

The Older Gentleman wrote:

> High Plains Thumper wrote:
>
>> Then I got a posting violation warning E-mail. All those messages
>> were deleted along with mine and replaced with this one by the
>> moderator.
>
> Jesus. How pathetic. Sounds like Krusty banning anyone who disagrees
> with his technical crap.....
>
> You were right to move on.

Yup. You were right about another point, shutting off the fuel petcock
to prevent any leaks caused by a defective fuel hose connection or fuel
hose.

I wish their forum good luck. Most people are keen to pick up on such
tactics and move on to other forums for advice.

[Tom $herman (-_-)]

Well, at least they did not suggest checking for fuel leaks with an open
flame.

I actually know of someone who did this (not on a motorcycle, but as
part of a pipeline rupture clean-up).

--
Tºm Shermªn - 42.435731°N, 83.985007°W
Post Free or Die!

[Polarhound]

Because 1 fuel auto-stop in the system is vastly better than two, right?

[David T. Johnson]

If the bike uses gravity feed, there needs to be a fuel petcock shutoff valve between the fuel and the carbs. Otherwise, the fuel will continue flowing very, very slowly as fuel evaporates in the carb bowl, migrates as a vapor through the throttle valve to the engine crankcase, or very slowly seeps as a liquid into the engine through the float valve (which is not designed to be a long-term tight shutoff valve). Just about any engine with gravity fuel feed has a petcock be it a generator, lawnmower (okay older, cheap mowers don't), boat, etc. Bikes used to have a manual petcock but riders often forgot to close it at the end of a ride so back in the early 1980s came the 'automatic' vacuum petcock which would close whenever the engine was not pulling a vacuum by pumping air through the intake valves. I have a 1983 Honda cx650 which still has the original vacuum petcock diaphragm still in working condition. However, there are rebuild kits and they are not hard to rebuild. I prefer a manual petcock but it's better to have the vacuum petcock than to have the manual and frequently forget to close it, thereby significantly shortening your engine life by reducing the lubricating ability of the crankcase oil. Gasoline gradually accumulates in the crankcase oil of any gasoline engine anyway which is one of the reasons for the mandatory oil change. (FYI, propane fueled engines have a much longer life span due to the better lubrication of the gasoline-free crankcase oil.) High Plains Thumper wrote: > I found this posted on a Suzuki LS650 Savage forum. This regards > replacing the OEM vacuum operated petcock with a manual petcock from a > Yamaha Raptor 660 ATV. Is this sound advice? > [quote] > To give you a numerical quantification on leakers, there has only been > two leaking float valve assemblies ever noted after changing over to a > Raptor, both of which had been leaking on those particular carburetors > since before the stock petcock was removed. In both cases the user > dropped the bowl and changed out the damaged float valve assembly. In > both cases, it was a simple mechanical problem with the carburetor that > was due to previous abuse. In neither case did any gasoline get into > the sump. > Remember, gasoline in the sump has NEVER YET HAPPENED due to a Raptor > petcock conversion, indeed the only gas in sump episodes of any severity > (such as could possibly result in a fire, etc.) have happened with the > stock vacuum actuated petcock diaphragm failing and running gas down the > vac line. > But we are all watching diligently for that first Raptor gas in sump > episode as logically it is a possibility, abet a slim one. > Fact is, you leave your Raptor on -- nothing bad happens. Some of us > (Serowbot, Oldfeller) leave our Raptors on all the time as a matter of > habit, only shutting it off for any long term storage periods. Raptors > don't cause any known failure modes that have any identifiable frequency > even when left on. > Vac petcocks however WILL FAIL INSIDE THEMSELVES DUE TO RUBBER AGEING on > a almost certainty basis over a 5-15 year period. Vac petcocks as a > separate system have 5 known failure modes and ARE KNOWN to put gasoline > down into the sump with some of them. > When using normal pump gasolines (not fancy nitro racing fuel) no Raptor > petcock has ever failed in 20 years and 100s of thousands of > installations on both RVs and Savages. They just work. > And if your float valve assembly isn't in sorry shape to begin with, > Raptors do work flawlessly in the Savage motorcycle. > [/quote] > http://suzukisavage.com/cgi-bin/YaBB.pl?num=1340099972 Posted with OS/2 Warp 4.52 and Sea Monkey 1.5a

[Klaus Cammin]

Hi High Plains Thumper,

I agree with the author of that quote. It is a bad idea in the first place to
use a vacuum driven petcock. A petcock is a simple mechanic part and should
be failproof.

The OEM cock of the Savage destroyed that feature due to complicated
additional technical parts and this clearly outweighs the possible benefits
of an automatic OFF. You have no trouble with a normal cock, and if the fuel
spills over in the carburator, it's a problem of the carb, not the cock.

With the OEM cock, there is a long and annoying period, when the rubber parts
start giving way, because the machine doesn't run properly any longer. One
day everything works fine, the other the bike will cough with lack of gas. :-
(

I changed to a Raptor cock on my Savage, too, and it's fine! :-)

> Then why do OEM's put a vacuum operated petcock that automatically shuts
> off the fuel when the engine is not operating?

Call me suspicious, but: a new petcock costs 80 Euro, you need 2 oder 3 in
the Savage's lifetime, what should a manufacturer complain about??

Viele Gr��e
Klaus

[High Plains Thumper]

Klaus Cammin wrote:
> Hi High Plains Thumper,
>
> I agree with the author of that quote. It is a bad idea in the first
> place to use a vacuum driven petcock. A petcock is a simple mechanic
> part and should be failproof.

My disagreement wasn't over usage of the Raptor petcock. I've used
mechanical ones and yes, they are very simple devices. My disagreement
was advice to leave the manual petcock ON when parked.

> The OEM cock of the Savage destroyed that feature due to complicated
> additional technical parts and this clearly outweighs the possible
> benefits of an automatic OFF.

My OEM Savage lasted 16 years. When it acted up, I had to place it on
PRIme until I replaced it. So it gave 16 years reliability. What's so
complex about a vacuum diaphragm that opens and closes a valve?

> You have no trouble with a normal cock, and if the fuel spills over
> in the carburator, it's a problem of the carb, not the cock.

So, by leaving the manual petcock in the ON position when parked, we are
going to blame the carburetor for the problem, if we experience
hydraulic lock when starting and wind up with a broken piston crown,
sheared starter gear, or worse?

No, the trouble is with the rider who did not exercise diligence in
TURNING OFF THE PETCOCK in the first place.

> With the OEM cock, there is a long and annoying period, when the
> rubber parts start giving way, because the machine doesn't run
> properly any longer. One day everything works fine, the other the
> bike will cough with lack of gas. :- (

How many years does it take to act up? I replaced the manual petcock on
my Honda CB100 eight years ago. Recently I replaced the seal, which had
deteriorated.

> I changed to a Raptor cock on my Savage, too, and it's fine! :-)

Well, good for you.

>> Then why do OEM's put a vacuum operated petcock that automatically
>> shuts off the fuel when the engine is not operating?
>

> Call me suspicious, but: a new petcock costs 80 Euro, you need 2 or

> 3 in the Savage's lifetime, what should a manufacturer complain
> about??

I never heard Suzuki complain. OEM parts will always be more expensive,
because the manufacturer must also factor in amortization of the
facility's rent, utilities, repairs, overhead such as salaries, facility
insurance, etc. for storing these parts over its anticipated shelf life.

I think the Raptor a good solution, because one can remove the tank
without disassembling the petcock from the tank, in order to remove the
tank. It was the other advice that I did not consider sound.

[High Plains Thumper]

On 07/15/2012 05:10 PM, Polarhound wrote:
> Because 1 fuel auto-stop in the system is vastly better than two,
> right?

Of course. That is why people replace fuses with paper clips, when the
fuse blows. The wire blows to protect the paper clip.

[Polarhound]

On 7/17/2012 7:12 PM, High Plains Thumper wrote:
> On 07/15/2012 05:10 PM, Polarhound wrote:
>> Because 1 fuel auto-stop in the system is vastly better than two,
>> right?
>
> Of course. That is why people replace fuses with paper clips, when the
> fuse blows. The wire blows to protect the paper clip.
>

Next time, try the foil out of a cigarette pack. Always good for
lighting up someone's life.

[High Plains Thumper]

Tom $herman wrote:
>
> I actually know of someone who did this (not on a motorcycle, but as
> part of a pipeline rupture clean-up).

Did he become a part of the clean up (a casualty)?

[Klaus Cammin]

Hallo High Plains Thumper,

High Plains Thumper wrote:
> My disagreement was advice to leave the manual petcock ON when parked.

Oh, I see, but I'm not quite sure, if that was the author's intention and
whether he(?) just wanted to state, that there's not much harm leaving it
in the ON-position all the time.

However, if it actually were a recommendation, I've no qualms agreeing to
your disagreement. Of course it's advisable to close the pertcock during
longer parking periods. I tend to forget it, but it hasn't been a problem
until now.

> What's so complex about a vacuum diaphragm that opens and closes a valve?

It's not just that. The system opens many opportunities for failure, not
only a disfunctional diaphragm and that little rubber ring inside not
closing or opening properly, but it's common that the vaccuum breaks down
or is too weak. Every now and then every Savage driver has problems with
the vaccum hose between petcock and carburetor, it's the first thing to
think of, when the engine runs poorly. I'm pretty glad, that there's no
need for that any longer.

Admitted, petcock replacement happens only once in 15 years, and that
appears bearable, but it wouldn't happen at all with a normal petcock. (Oh,
just reading it happenend to you on your CB100 ... ;-)

> So, by leaving the manual petcock in the ON position when parked, we are
> going to blame the carburetor for the problem, if we experience
> hydraulic lock when starting and wind up with a broken piston crown,
> sheared starter gear, or worse?
>
> No, the trouble is with the rider who did not exercise diligence in
> TURNING OFF THE PETCOCK in the first place.

I doubt, if we can blame the petcock's ON-position either. Before we
experience these horrible damages, shouldn't we notice lesser hints, that
something is wrong? (I'm not sure, whether a defective carb valve would
produce a fuel puddle beneath the bike.) And isnt't it possible, that we
fail to detect those, because the petcock is OFF, either automatically or
manually? Again, one really should close the petcock, especially when you
don't ride the bike for several days.

> I think the Raptor a good solution, because one can remove the tank
> without disassembling the petcock from the tank, in order to remove the
> tank.

True, tank removal is much easier with the Raptor petcock, though I've
already done this with the unremoved OEM tap. It's just a little trickier.

So, I think no need to quarrel about something, that might turn out as the
emperor's new clothes. Everybody should be happy with his setting. :-)

So long

Viele Gr��e
Klaus

[Tom $herman (-_-)]

On 7/18/2012 7:36 AM, High Plains Thumper wrote:
> Tom $herman wrote:
>>
>> I actually know of someone who did this (not on a motorcycle, but as
>> part of a pipeline rupture clean-up).
>
> Did he become a part of the clean up (a casualty)?
>

Amazingly, he kept his job.