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From: Mark Olson on 6 Jul 2006 14:17
nomorespameventhoughthejapanesespamgivesmeachuckle <nousenetspam(a)gmail.com> wrote:

> Fuel is leaking from the carbs because the vacuum is not operating
> which means the petcock is effectively in the prime position. This
> would be the same as having just an inline fuel valve with a simple
> on/off switch and leaving it in the on position overnight. You too
> would wake up in the morning with flooded carbs; it has nothing to do
> with the floats or needle valves since the gravity is forcing the fuel
> into the carbs whether they are asking for it or not.

Please enlighten us- how does a carb 'ask for' fuel?

If carbs are overflowing grossly, their inlet valves are not working
properly, which, for the hard of thinking, is a totally independent
fault from a leaky petcock, vacuum or otherwise.

Yes, vacuum petcocks exist because carbs can be operating properly yet
still leak *a bit* of fuel past their float valves, but carbs in good
condition can and do tolerate fuel pressure (from a gravity feed system)
indefinitely. My '77 KZ650B1 and '81 CM400T carbs never overflowed
despite forgetting to turn the petcock off on numerous occasions.

--
'01 SV650S '99 EX250-F13 '98 ZG1000A-13 '81 CM400T
OMF #7
From: nomorespameventhoughthejapanesespamgivesmeachuckle on 6 Jul 2006 16:55

Mark Olson wrote:
> nomorespameventhoughthejapanesespamgivesmeachuckle <nousenetspam(a)gmail.com> wrote:
>
> > Fuel is leaking from the carbs because the vacuum is not operating
> > which means the petcock is effectively in the prime position. This
> > would be the same as having just an inline fuel valve with a simple
> > on/off switch and leaving it in the on position overnight. You too
> > would wake up in the morning with flooded carbs; it has nothing to do
> > with the floats or needle valves since the gravity is forcing the fuel
> > into the carbs whether they are asking for it or not.
>
> Please enlighten us- how does a carb 'ask for' fuel?
>
> If carbs are overflowing grossly, their inlet valves are not working
> properly, which, for the hard of thinking, is a totally independent
> fault from a leaky petcock, vacuum or otherwise.
>
> Yes, vacuum petcocks exist because carbs can be operating properly yet
> still leak *a bit* of fuel past their float valves, but carbs in good
> condition can and do tolerate fuel pressure (from a gravity feed system)
> indefinitely. My '77 KZ650B1 and '81 CM400T carbs never overflowed
> despite forgetting to turn the petcock off on numerous occasions.
>
> --
> '01 SV650S '99 EX250-F13 '98 ZG1000A-13 '81 CM400T
> OMF #7

Carbs ask for fuel by the floats lowering when the fuel supply in the
float bowl gets low. This in turn opens the float valve letting more
fuel in. Since the carbs are full, the float would normally not sink,
and therefore the carbs wouldn't "ask" for any more fuel. Since the
petcock is bad, fuel is forced down into the cabs whether it wants them
or not.



If I put three and three together:

Before last week my petcock didn't leak and neither did my carbs.

Then my petcock started to slightly leak (drip drip) leak if I took the
tube off the tank; only my fourth carb leaked.

Now my petcock really leaks (constant flow); now all my carbs leak.

It sure seems to be a problem with the petcock and not the carbs.


The carbs do not leak out of the breather, but instead the leak is
seeping out of the drain-screw in the float bowl and is making its way
past the gasket between the carb body and float bowl.

Hope this makes sense.

From: nomorespameventhoughthejapanesespamgivesmeachuckle on 6 Jul 2006 21:35
Here is an update:

I drained the fuel tank; took apart the petcock and rebuilt it.

I attached the petcock to the tank and refilled with a gallon or two.

I let it sit for hours, moved it all around, and nothing leaked from
the petcock.

Then as a test I put the tank on the bike and attached only the vacuum
hose. The petcock is "ON."
I then turned the engine over a few times and gas came out.
After turning over the engine, gas continues to drip out the petcock
(drip drip drip) and never stops dripping.
So now I can take the gas tank off the bike and set it on a bench and
the petcock will continue to drip.
If I take the petcock apart and put it back together I get no drips...

So the problem seems to stem from after I crank the engine and a vacuum
is created. Is the vacuum dislodging something in the petcock? Is the
plunger/diaphragm not re-seating correctly after a vacuum is initiated?
Any ideas?

From: Rob Kleinschmidt on 6 Jul 2006 22:09

nomorespameventhoughthejapanesespamgivesmeachuckle wrote:
> Since the carbs are full, the float would normally not sink,
> and therefore the carbs wouldn't "ask" for any more fuel. Since the
> petcock is bad, fuel is forced down into the cabs whether it wants them
> or not.

Without a fuel pump, fuel is not "forced" into the carbs.

There's nothing forcing the fuel anywhere except gravity.
The carb floats should prevent fuel from flowing into the carbs.
If they're not doing this, it's likely that there's also a problem
in the floats and/or float valves.

I guess theoretically all you problems could be caused by
lots of rust or dirt crapping up the shutoff mechanisms, but
what it sounds like is that your carb floats weren't working
right and the petcock was the only thing preventing flooding.

Since you're in there anyway, you ought to look for dirt
and rust in the tank and consider new floats and/or float
valves.

From: Beto on 6 Jul 2006 22:31
On 6 Jul 2006 13:55:20 -0700,
"nomorespameventhoughthejapanesespamgivesmeachuckle" <nousenetspam(a)gmail.com>
wrote:

>
>Mark Olson wrote:
>> nomorespameventhoughthejapanesespamgivesmeachuckle <nousenetspam(a)gmail.com> wrote:
>>
>> > Fuel is leaking from the carbs because the vacuum is not operating
>> > which means the petcock is effectively in the prime position. This
>> > would be the same as having just an inline fuel valve with a simple
>> > on/off switch and leaving it in the on position overnight. You too
>> > would wake up in the morning with flooded carbs; it has nothing to do
>> > with the floats or needle valves since the gravity is forcing the fuel
>> > into the carbs whether they are asking for it or not.
>>
>> Please enlighten us- how does a carb 'ask for' fuel?
>>
>> If carbs are overflowing grossly, their inlet valves are not working
>> properly, which, for the hard of thinking, is a totally independent
>> fault from a leaky petcock, vacuum or otherwise.
>>
>> Yes, vacuum petcocks exist because carbs can be operating properly yet
>> still leak *a bit* of fuel past their float valves, but carbs in good
>> condition can and do tolerate fuel pressure (from a gravity feed system)
>> indefinitely. My '77 KZ650B1 and '81 CM400T carbs never overflowed
>> despite forgetting to turn the petcock off on numerous occasions.
>>
>> --
>> '01 SV650S '99 EX250-F13 '98 ZG1000A-13 '81 CM400T
>> OMF #7
>
>Carbs ask for fuel by the floats lowering when the fuel supply in the
>float bowl gets low. This in turn opens the float valve letting more
>fuel in. Since the carbs are full, the float would normally not sink,
>and therefore the carbs wouldn't "ask" for any more fuel. Since the
>petcock is bad, fuel is forced down into the cabs whether it wants them
>or not.
>
No No No !!!!!!!!
>
>
>If I put three and three together:
>
>Before last week my petcock didn't leak and neither did my carbs.
>
>Then my petcock started to slightly leak (drip drip) leak if I took the
>tube off the tank; only my fourth carb leaked.
>
>Now my petcock really leaks (constant flow); now all my carbs leak.
>
>It sure seems to be a problem with the petcock and not the carbs.
>
>
>The carbs do not leak out of the breather, but instead the leak is
>seeping out of the drain-screw in the float bowl and is making its way
>past the gasket between the carb body and float bowl.
>
>Hope this makes sense.

Do you have crud in the gas tank?

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