Emission Controls

C

cesar carrasco

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Sep 7, 2017
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Hello fellow GMCer's, I just recently bought two GMC RV's. One is a 1973 23' Sequoia, the other is a 1974 26' Glacier(both are in the registry).
The Sequoia (66k miles) had the motor, trans and final drive rebuilt, it has a holly carb and headers; and what from what I can see it doesn't have
the emission control parts. The Glacier (51k miles) appears to be all original. I live in Riverside California and both RV's are exempt from smog
checks. I would like to get your thoughts on whether or not to remove the emissions controls. For example the distributor spark retarding vacuum,
etc. and any others you may or may not recommend.

What are the pros and cons?
 
> Hello fellow GMCer's, I just recently bought two GMC RV's. One is a 1973 23' Sequoia, the other is a 1974 26' Glacier(both are in the registry).
> The Sequoia (66k miles) had the motor, trans and final drive rebuilt, it has a holly carb and headers; and what from what I can see it doesn't have
> the emission control parts. The Glacier (51k miles) appears to be all original. I live in Riverside California and both RV's are exempt from smog
> checks. I would like to get your thoughts on whether or not to remove the emissions controls. For example the distributor spark retarding vacuum,
> etc. and any others you may or may not recommend.
>
> What are the pros and cons?

Cesar,

Even in California, a '73 had almost no emission controls.
There are really two that I know of only because my coach lived in California a while and had to be converted to CARB standards to be registered.

One is the double charcoal canister. That caused me untold grief until I removed the added can. You do want the one can as that is where the air
goes in to replace the fuel drawn out. If you disassemble the parts it is pretty clear how to take that bottom can out.

The other is the TVS Thermal Vacuum Switch. This sends vacuum from the ported tap on the carburetor to the distributor at idle and changes to a
manifold port if the engine gets too hot. This speeds up the engine so it both pumps more coolant and the fan pulls more air. Part of the reason the
engine gets too hot at idle is because it is running with the timing too far retarded. If you disconnect the TVS and lead the manifold vacuum to the
distributor, you will have to back the idle off at the carburetor to get it to be rational again. I did this and mine runs just fine that way.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Are you sure these units do not have an extra 100,000 miles on them.

On Mon, Oct 16, 2017 at 4:14 PM, Cesar Carrasco
wrote:

> Hello fellow GMCer's, I just recently bought two GMC RV's. One is a 1973
> 23' Sequoia, the other is a 1974 26' Glacier(both are in the registry).
> The Sequoia (66k miles) had the motor, trans and final drive rebuilt, it
> has a holly carb and headers; and what from what I can see it doesn't have
> the emission control parts. The Glacier (51k miles) appears to be all
> original. I live in Riverside California and both RV's are exempt from smog
> checks. I would like to get your thoughts on whether or not to remove the
> emissions controls. For example the distributor spark retarding vacuum,
> etc. and any others you may or may not recommend.
>
> What are the pros and cons?
>
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--

*John Phillips*
 
Thank you Matt. It's just one more thing to eliminate when I'm trouble shooting the engines. They both run good, but not yet 100%.

John, the 23 footer came with plenty of documentation. The 26 footer came with not much documentation. Both do appear to have sat out in the open air for many years and both odometers appear to work properly. No water leaks or damage.

Sent from my iPhone

>
> Are you sure these units do not have an extra 100,000 miles on them.
>
> On Mon, Oct 16, 2017 at 4:14 PM, Cesar Carrasco

>
>> Hello fellow GMCer's, I just recently bought two GMC RV's. One is a 1973
>> 23' Sequoia, the other is a 1974 26' Glacier(both are in the registry).
>> The Sequoia (66k miles) had the motor, trans and final drive rebuilt, it
>> has a holly carb and headers; and what from what I can see it doesn't have
>> the emission control parts. The Glacier (51k miles) appears to be all
>> original. I live in Riverside California and both RV's are exempt from smog
>> checks. I would like to get your thoughts on whether or not to remove the
>> emissions controls. For example the distributor spark retarding vacuum,
>> etc. and any others you may or may not recommend.
>>
>> What are the pros and cons?
>>
>>
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
>
> --
>
> *John Phillips*
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
>
> ​My feeling is that more you understand the emission system on our
> coach,more you appreciate what they did.
>
​We get in coaches where po have tried to eliminate the system without
fully understand what each does.​

​The end results are seldom good.​

​
>
>
 
Jim, are there any other publications on the emission system other than the
maintenance manuals?

> >
> > ​My feeling is that more you understand the emission system on our
> > coach,more you appreciate what they did.
> >
> ​We get in coaches where po have tried to eliminate the system without
> fully understand what each does.​
>
> ​The end results are seldom good.​
>
>
> ​
> >
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
​I'm sure there is, but they never explain it all as it is written for
people that are in the business and know enough about each.​
I'm in a middle of working on an Air Filter Housing job for Tesla so I will
look them up and we can discuss it then.
Get me your email address.

On Mon, Oct 16, 2017 at 9:10 PM, Cesar Carrasco
wrote:

> Jim, are there any other publications on the emission system other than the
> maintenance manuals?
>
>
>
> On Mon, Oct 16, 2017 at 9:04 PM, Jim Kanomata

>
> > >
> > > ​My feeling is that more you understand the emission system on our
> > > coach,more you appreciate what they did.
> > >
> > ​We get in coaches where po have tried to eliminate the system without
> > fully understand what each does.​
> >
> > ​The end results are seldom good.​
> >
> >
> > ​
> > >
> > >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
My email address is: ccarrasco2013

Thanks again Jim.

> ​I'm sure there is, but they never explain it all as it is written for
> people that are in the business and know enough about each.​
> I'm in a middle of working on an Air Filter Housing job for Tesla so I will
> look them up and we can discuss it then.
> Get me your email address.
>
> On Mon, Oct 16, 2017 at 9:10 PM, Cesar Carrasco

>
> > Jim, are there any other publications on the emission system other than
> the
> > maintenance manuals?
> >
> >
> >
> > On Mon, Oct 16, 2017 at 9:04 PM, Jim Kanomata

> >
> > > >
> > > > ​My feeling is that more you understand the emission system on our
> > > > coach,more you appreciate what they did.
> > > >
> > > ​We get in coaches where po have tried to eliminate the system without
> > > fully understand what each does.​
> > >
> > > ​The end results are seldom good.​
> > >
> > >
> > > ​
> > > >
> > > >
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> > >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
>
>
>
> --
> Jim Kanomata
> Applied/GMC, Newark,CA
> jimk
> http://www.appliedgmc.com
> 1-800-752-7502
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Learn each system and what they do. There was no A.I.R. or exhaust heat riser on a GMC and it predated. EGR and Cats started fully in 75 but was
exempt due to GVW
Non Calif emissions had:
1)Evaporative emissions- a great thing with self regenerating charcoal to catch vapors and reburn. Could only imcrease mileage by minimiziing evap and

Reburning
2) Early fuel evaporation or called AC AutoThermAC carb air preheat. This blended hot and cold air to keep intake air at about 115F. This helped
during warmup cycle and minimized fuel pooling and cyl washdown. It kept the air to the Qjet at a more consistent temp so the engineers could tune
slightly leaner without drivability issues as fuel vaporized more easily. Under heavy throttle the blend door motor has low vacuum signal so the
spring returns it to full cold air so no performance downside. In warm weather it is wide open anyway due to high underhood temps.
3) TVS Thermal Vacuum Switch. Allows ported vac signal to distributor 99% of time. If coolant gets over 220F the switch snaps and sends manifold vac
to the dist. This picks up idle speed if in a traffic jam etc and aides cooling. My GMC runs cool at idle in extreme temps simply because there is no
road load heat to disipate. This only actvated once or twice when a traffic jam happened immediately after high speed cruise and road load heat did
not have time to shed. A great device in this situation. It worked great, then after a few minutes the switch snapped back to ported and idled dropped
slightly.

Calif vehicles had a second charcoal canister as well as a complicated throttle kicker setup to control idle speed. They also had specifc Calif carbs
and distributors. Someone else will have to chime in on these as mine is Federal and never laid eyes on one.
I see only good reasons to keep 1,2,and 3 above as good running and low emissions usually run hand in hand. If you are misfiring during warmup you are
poluting air and your oil. If you are overheating your NOX emmisions may go high.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Also if you have to come to a quick stop with a highway traffic jam on a 100deg day, and the TVS picks up the idle, a secondary advantage is your dash
air will work better and the higher fan speed will help the High Side pressures from going extreme.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
John, thank you for your valuable information, I greatly appreciate it. My main concern was the retarding and advancing of the timing and potential overheating damage if the TVS switch fails.

Cesar

Sent from my iPhone

>
> Also if you have to come to a quick stop with a highway traffic jam on a 100deg day, and the TVS picks up the idle, a secondary advantage is your dash
> air will work better and the higher fan speed will help the High Side pressures from going extreme.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
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