Vapor canister

[gene]

Have several questions about the vapor recovery canister under the
passenger side.

1) Is it possible to suck a vacuum on the gas tanks through this unit. Is
there a relief or a valve that stops this if there is a failure.

2) Can we remove the vacuum connection all together if we are in a non
smog state?

3) Are the California coaches different than the non CA coaches in this unit?

Thanks, I am installing a Howell TBI and I hope to make this vacuum leak go
away.

gene
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/

 

[dave1]

>2) Can we remove the vacuum connection all together if we are in a non
>smog state? .... Thanks, I am installing a Howell TBI and I hope to make=20
>this vacuum leak go
>away.

I would suggest leaving it in place. Fuel injection systems circulate fuel=
=20
through the injectors to keep them cool. The warm fuel is returned to the=20
tanks. Warm fuel generates fumes more rapidly than cool fuel. I suspect=20
that you will be exposing yourself, your family and neighbors to a rather=20
high level of harmful fuel vapor each time you shutdown. The charcoal=20
canister is reasonably cheap and pretty reliable. If you think you are=20
having problems with it, I would suggest replacing it. Especially if you=20
are switching to fuel injection.

Also, keep in mind that the Howell TBI system is a closed loop system. It=20
will be more tolerant of vacuum leaks. It compensates by adding more fuel=20
to the mix so the mixture stays on target. It also adjusts the idle air=20
bypass to keep the idle speed right on target.

I know this for a fact because the previous owner installed a vacuum=20
operated axillary air pump. When I used the air pump with the carb, it=20
would not idle well at all. When using the air pump with the Howell TBI=20
system I cant even tell that its running. The Howell system adjusts for the=
=20
additional air in the manifold and you never know the difference.

Dave
Ann Arbor, MI.
73 Sequoia (26'/455/EFI/HEI/160=B0)

 

[gene]

thanks-- what I am not sure of is how large a vac leak this is or if it can
draw a vac on the gas tank
gene

>>2) Can we remove the vacuum connection all together if we are in a non
>>smog state? .... Thanks, I am installing a Howell TBI and I hope to make=
=20
>>this vacuum leak go
>>away.
>
>I would suggest leaving it in place. Fuel injection systems circulate fuel=
=20
>through the injectors to keep them cool. The warm fuel is returned to the=
=20
>tanks. Warm fuel generates fumes more rapidly than cool fuel. I suspect=20
>that you will be exposing yourself, your family and neighbors to a rather=
=20
>high level of harmful fuel vapor each time you shutdown. The charcoal=20
>canister is reasonably cheap and pretty reliable. If you think you are=20
>having problems with it, I would suggest replacing it. Especially if you=20
>are switching to fuel injection.
>
>Also, keep in mind that the Howell TBI system is a closed loop system. It=
=20
>will be more tolerant of vacuum leaks. It compensates by adding more fuel=
=20
>to the mix so the mixture stays on target. It also adjusts the idle air=20
>bypass to keep the idle speed right on target.
>
>I know this for a fact because the previous owner installed a vacuum=20
>operated axillary air pump. When I used the air pump with the carb, it=20
>would not idle well at all. When using the air pump with the Howell TBI=20
>system I cant even tell that its running. The Howell system adjusts for the=
=20
>additional air in the manifold and you never know the difference.
>
>
>Dave
>Ann Arbor, MI.
>73 Sequoia (26'/455/EFI/HEI/160=B0)
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/

 

[dave1]

>thanks-- what I am not sure of is how large a vac leak this is or if it can
>draw a vac on the gas tank

I don't know what changes they made over the years to the charcoal=20
canister but the one I have on my 73 is pretty dumb. I think it works a lot=
=20
like a PCV valve (high vac low flow and low vac high flow). The idea=
is=20
to pull a lot of purge air through the charcoal when the engine is under=
load.

I suppose there is the possibility that it could pull a vacuum on the fuel=
=20
tanks if the charcoal was blocked up. Its easy enough to tell if this is=20
happening. When you stop for fuel, keep the engine running and listen when=
=20
you take off the fuel cap. If there is a big rush of air into the fuel=20
tanks then the vapor recovery system is blocked (or pulling a vacuum).


Dave
Ann Arbor, MI.
73 Sequoia (26'/455/EFI/HEI/160=B0)

 

[gene]

great..... I just do not know what the inside of the canister looks like.
book does not show much, and I am not going to mess with it unless it gives
problems.

thanks
gene

>
>> thanks-- what I am not sure of is how large a vac leak this is or if it can
>> draw a vac on the gas tank
>
>Gene,
> It's not a vacuum "leak" at all. The carburetor was designed to have a
>certain amount of air from the vapor cannister drawn into it when cruising.
>Should have no ill effect on performance. Even in my "clean air be damned"
>youth, I never considered removing the vapor recovery system, as it cleans
>the air without pain, and the sealed tank, pressure vent, vapor separator
and
>all that actually help prevent vapor lock (by keeping slight positive
>pressure in the tank), and prevent loss of fuel out the vent.
> There is no way it could "draw a vac(uum) on the gas tank" unless the
>vapor cannister were TOTALLY clogged (unlikely) or the hoses were badly
>misconnected.
> BTW, even with a clogged vent, you're only likely to draw a vacuum in the
>tank in cold weather. Otherwise, the vapor pressure of the fuel usually
>keeps things under pressure.
> My .02. HTH.
>
>Rick Staples
>'75 Eleganza
>Louisville, CO
>
Genef -- 77PB/ore/ca
GMC MOTORHOME INFORMATION
mr.erf
http://www.california.com/~eagle/

 

[bartz paul]

All that is in the canister, outside of the filter at the bottom, is a
quantity of hard granular carbon chips, about double or triple the size of
coffee granules. I opened mine a number of years ago, in fact some of it
dumped out on the driveway. I just scoped it back into the canister. It
wasn't real soft and didn't rub of on my hands.

Paul Bartz

From: gene [mailto:mr.erf]
Sent: Tuesday, December 14, 1999 10:53 PM

great..... I just do not know what the inside of the canister looks like.
book does not show much, and I am not going to mess with it unless it gives
problems.
thanks
gene

>In a message dated 12/14/99 9:32:33 AM MDT, mr.erf

>
>> thanks-what I am not sure of is how large a vac leak this
is or if it can
>> draw a vac on the gas tank
>
>Gene,
> It's not a vacuum "leak" at all. The carburetor was designed to
have a
>certain amount of air from the vapor cannister drawn into it when
cruising.
>Should have no ill effect on performance. Even in my "clean air be
damned"
>youth, I never considered removing the vapor recovery system, as it
cleans
>the air without pain, and the sealed tank, pressure vent, vapor
separator
and
>all that actually help prevent vapor lock (by keeping slight
positive
>pressure in the tank), and prevent loss of fuel out the vent.
> There is no way it could "draw a vac(uum) on the gas tank"
unless the
>vapor cannister were TOTALLY clogged (unlikely) or the hoses were
badly
>misconnected.
> BTW, even with a clogged vent, you're only likely to draw a
vacuum in the
>tank in cold weather. Otherwise, the vapor pressure of the fuel
usually
>keeps things under pressure.
> My .02. HTH.
>
>Rick Staples