Home » Public Forums » GMCnet » 403 Dual Vacuum Advance (California Emissions)
| 403 Dual Vacuum Advance (California Emissions) [message #318429] |
Sat, 03 June 2017 20:31  |
Ty Hardiman
Messages: 43
Registered: April 2017
Location: Norman, Oklahoma
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Working through the vacuum system, I have a question. This is a 1977 California emissions 403 and the maintenance manual shows (and I have) a dual-vacuum distributor advance. I think the second vac line is to retard the timing, however that line has been disconnected from the christmas tree TVS valves (California has two) and directly connected to the carb. So it looks like I'm running full vac to the advance and retard side simultaneously. The previous owner completely abandoned both of the TVS valves which is why I am tracing the vacuum system in the first place. Should I eliminate the vacuum line to the second port?
Norman, OK / August 1977 Kingsley / 403 / 3.55 / 16" / Quadrajet
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| Re: 403 Dual Vacuum Advance (California Emissions) [message #318431 is a reply to message #318429] |
Sat, 03 June 2017 21:36  |
Ty Hardiman
Messages: 43
Registered: April 2017
Location: Norman, Oklahoma
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Sorry, I should clarify that the primary/advance vacuum line goes to the front, drivers side connection on the carb, and the second/retard? vacuum line goes to the manifold and T's with the HVAC vacuum/canister line.
Norman, OK / August 1977 Kingsley / 403 / 3.55 / 16" / Quadrajet
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| Re: [GMCnet] 403 Dual Vacuum Advance (California Emissions) [message #318433 is a reply to message #318431] |
Sat, 03 June 2017 22:10 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Best to replace the Vac unit with the single unit and hook it up like the
earlier unit with Thermostatic switch.
Should you need help, call .
On Sat, Jun 3, 2017 at 7:36 PM, Ty Hardiman wrote:
> Sorry, I should clarify that the primary/advance vacuum line goes to the
> front, drivers side connection on the carb, and the second/retard? vacuum
> line goes to the manifold and T's with the HVAC vacuum/canister line.
> --
> Ty hardiman, Norman, OK
> 1977 Kingsley TZE167V102390
> Build date August 1977
> 26'/403 CI/16" Wheels/Quadrajet/hei
> Previous Owners: Basil LeBlanc, Dan Ramker
> Original owner: William Strahm, Loveland, CO
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
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--
Jim Kanomata
Applied/GMC, Newark,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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Jim Kanomata
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jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: 403 Dual Vacuum Advance (California Emissions) [message #318461 is a reply to message #318429] |
Sun, 04 June 2017 13:13 |
Ty Hardiman
Messages: 43
Registered: April 2017
Location: Norman, Oklahoma
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Thank for the answers so far. I am always prepared to be wrong, to have done a poor job wording my question, or to just not understand the problem well enough to ask the right question.
I created an album showing the California dual-vacuum timing advance as I understand it. It includes the schematic from my manual, and a picture of my distributor vac advance.
http://www.gmcmhphotos.com/photos/g7047-dual-vacuum-distributor.html
As I understand JimK, he suggested replacing the vacuum advance with a single port and going back to the TVS. Coincidentally I was on the phone with Dick Patterson two days ago discussing a different issue, but related to the distributor. Probably time to order a Springfield dist. from Applied. Part of the issue here is that I don't understand the reason for the TVS. Also I don't understand the difference between a vacuum port on the carb vs on the manifold. Also I don't know if I should leave the system as-is until I get a replacement single port advance, or cap the second (retard?) port on the advance.
Thanks all,
Ty
Norman, OK / August 1977 Kingsley / 403 / 3.55 / 16" / Quadrajet
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| Re: [GMCnet] 403 Dual Vacuum Advance (California Emissions) [message #318464 is a reply to message #318450] |
Sun, 04 June 2017 13:30 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Ken, the parts book no. Are only 20% worthwhile.
I believe I can see what # we carry.
You know where I hang out.😐
Sent from my iPhone
> On Jun 4, 2017, at 8:39 AM, James Hupy wrote:
>
> If your ignition has 2 vacuum canisters, It is not from a 77 California
> Equipped 403 as fitted originally in a GMC motor home.
> Jim Hupy
>
> On Jun 3, 2017 10:47 PM, "Ken Burton" wrote:
>
> I went looking for that vacuum advance on line because I have never seen
> one. I could not find one. Maybe I should look in the original GMC parts
> book.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
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Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] 403 Dual Vacuum Advance (California Emissions) [message #318468 is a reply to message #318461] |
Sun, 04 June 2017 13:49 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Ohhhh Kkkkkk. There are very distinct differences between the 49 states 403
engine controls in 1977 vs 1978. Also, there are a TON of differences
between the California equipped 403 engines in 1977 and 1978.
Basically, consider them to be 4 distinct incarnations. 77 49
states, 77 California. 78 49 states, and 78 California. Fuel tank vents,
Charcoal canisters, Carbs, Distributors, TVS (Christmas trees) vacuum hose
routing, and the list gets longer from there.
IF, you have a California equipped coach, and you are in California
and need to get it smogged to purchase license plates, then all of the
original equipment fitted to the coach has to remain intact when it is
inspected. If you are located in a non-smogged state, then, you must meet
49 states requirements. I am unfamiliar with emissions requirements in
Oklahoma, so I can't help very much with your specific coach. I have a 49
states 1978 403 equipped coach, and most of the original equipment is
intact. Jim K. is a approved California Emissions guy, and he
frequently helps coaches pass emissions testing. Give him a call, see what
he comes up with.
Jim Hupy
Salem, Or
On Jun 4, 2017 11:14 AM, "Ty Hardiman" wrote:
> Thank for the answers so far. I am always prepared to be wrong, to have
> done a poor job wording my question, or to just not understand the problem
> well enough to ask the right question.
>
> I created an album showing the California dual-vacuum timing advance as I
> understand it. It includes the schematic from my manual, and a picture of my
> distributor vac advance.
>
> http://www.gmcmhphotos.com/photos/g7047-dual-vacuum-distributor.html
>
> As I understand JimK, he suggested replacing the vacuum advance with a
> single port and going back to the TVS. Coincidentally I was on the phone
> with
> Dick Patterson two days ago discussing a different issue, but related to
> the distributor. Probably time to order a Springfield dist. from Applied.
> Part of the issue here is that I don't understand the reason for the TVS.
> Also I don't understand the difference between a vacuum port on the carb vs
> on the manifold. Also I don't know if I should leave the system as-is
> until I get a replacement single port advance, or cap the second (retard?)
> port
> on the advance.
>
> Thanks all,
> Ty
> --
> Ty hardiman, Norman, OK
> 1977 Kingsley TZE167V102390
> Build date August 1977
> 26'/403 CI/16" Wheels/Quadrajet/hei
> Previous Owners: Basil LeBlanc, Dan Ramker
> Original owner: William Strahm, Loveland, CO
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
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| Re: [GMCnet] 403 Dual Vacuum Advance (California Emissions) [message #318469 is a reply to message #318461] |
Sun, 04 June 2017 13:56 |
jimk
Messages: 6734
Registered: July 2006
Location: Belmont, CA
Karma: 9
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Senior Member |
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Ty,
The TVS serves to increase the RPM of the engine at idle when the engine
starts overheating in traffic by receiving full vac from the intake
manifold.
Once it reaches standard operating temp, the valve pulls Throttle Vacuum,
which is more responsive at acceleration.
There are times this is needed, lot feel otherwise.
On Sun, Jun 4, 2017 at 11:13 AM, Ty Hardiman wrote:
> Thank for the answers so far. I am always prepared to be wrong, to have
> done a poor job wording my question, or to just not understand the problem
> well enough to ask the right question.
>
> I created an album showing the California dual-vacuum timing advance as I
> understand it. It includes the schematic from my manual, and a picture of my
> distributor vac advance.
>
> http://www.gmcmhphotos.com/photos/g7047-dual-vacuum-distributor.html
>
> As I understand JimK, he suggested replacing the vacuum advance with a
> single port and going back to the TVS. Coincidentally I was on the phone
> with
> Dick Patterson two days ago discussing a different issue, but related to
> the distributor. Probably time to order a Springfield dist. from Applied.
> Part of the issue here is that I don't understand the reason for the TVS.
> Also I don't understand the difference between a vacuum port on the carb vs
> on the manifold. Also I don't know if I should leave the system as-is
> until I get a replacement single port advance, or cap the second (retard?)
> port
> on the advance.
>
> Thanks all,
> Ty
> --
> Ty hardiman, Norman, OK
> 1977 Kingsley TZE167V102390
> Build date August 1977
> 26'/403 CI/16" Wheels/Quadrajet/hei
> Previous Owners: Basil LeBlanc, Dan Ramker
> Original owner: William Strahm, Loveland, CO
>
> _______________________________________________
> 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@appliedairfilters.com
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
Jim Kanomata
Applied/GMC
jimk@appliedairfilters.com
www.appliedgmc.com
1-800-752-7502
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| Re: [GMCnet] 403 Dual Vacuum Advance (California Emissions) [message #318470 is a reply to message #318461] |
Sun, 04 June 2017 13:51 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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What a rat's nest! Guess I never looked at that diagram before -- or just
blanked it out as too painful!
Pretty obvious how desperate the GM engineers had become in trying to meet
the new EPA rules. I won't pretend to try to figure it all out. IIWM,
(If It Was Me) I'd definitely do as you've postulated: Get a Dick Paterson
distributor and connect it to the manifold after removing all that other
in-the-way-waiting-to-give-trouble junk. (Unless Dick says hook to ported
vacuum on the carb).
Ken H.
On Sun, Jun 4, 2017 at 2:13 PM, Ty Hardiman wrote:
> ...
>
> I created an album showing the California dual-vacuum timing advance as I
> understand it. It includes the schematic from my manual, and a picture of my
> distributor vac advance.
>
> http://www.gmcmhphotos.com/photos/g7047-dual-vacuum-distributor.html
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: 403 Dual Vacuum Advance (California Emissions) [message #318475 is a reply to message #318461] |
Sun, 04 June 2017 15:05 |
 |
Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Ty Hardiman wrote on Sun, 04 June 2017 14:13Thank for the answers so far. I am always prepared to be wrong, to have done a poor job wording my question, or to just not understand the problem well enough to ask the right question.
I created an album showing the California dual-vacuum timing advance as I understand it. It includes the schematic from my manual, and a picture of my distributor vac advance.
http://www.gmcmhphotos.com/photos/g7047-dual-vacuum-distributor.html
As I understand JimK, he suggested replacing the vacuum advance with a single port and going back to the TVS. Coincidentally I was on the phone with Dick Patterson two days ago discussing a different issue, but related to the distributor. Probably time to order a Springfield dist. from Applied. Part of the issue here is that I don't understand the reason for the TVS. Also I don't understand the difference between a vacuum port on the carb vs on the manifold. Also I don't know if I should leave the system as-is until I get a replacement single port advance, or cap the second (retard?) port on the advance.
Thanks all,
Ty
Ty,
That diagram is amazing and it is typical of what we were going through (Thank Edmond Muskie) in the 70's when emission rules were suddenly tightened another 80%.
I will explain the TVS as best I can.
The H port at the carburetor base is what is called ported vacuum. It is local ambient when the throttle is closed, but quickly transitions to manifold vacuum with the opening of the throttle. This can make for very nice driveability. That means no flat spots or transition problems.
Emissions people like this a lot because the engine idles with much higher airflow so HC looks lower on a meter. Unfortunately, it also means that the engine working harder to make the power required to keep a stable idle speed. That makes it hotter and with the engine at idle speed, it can't pump water and air well enough to cool itself. So, since "hot" was not part of a driving cycle test, they take advantage of the fact and move the timing control to the B port which is manifold vacuum that is high at idle and this will cause the engine to speed up. Now it can cool itself.
Many people run effective with the distributor advance connected to either the H port (ported) or the B port (manifold) and each can be made to work. With older systems, (before what you have) the ported vacuum can have the advantage as noted above. But, if just a few things are changed (like the entire timing curve from Dick Paterson) then the manifold may be the better choice.
If you would like, you and I can sit down at Elkhart and I can explain the function of each part of the diagram you posted until the beer runs out. It had too functions that are actually only for simple (as in PPM) emissions. One was a hold on the advance for low speed to make the driver use more throttle and make the shift speed higher. The other was to prevent the rich mixture that used to occur in engine braking or overrun. (Emission people think brakes are cheap.)
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: 403 Dual Vacuum Advance (California Emissions) [message #318484 is a reply to message #318461] |
Sun, 04 June 2017 20:51 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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The following was received by me from Dick Paterson with a note that said I could post it if it appeared useful:
The 2 port cans were yet another attempt at meeting epa regs while trying to maintain best driveability, idle quality, etc, etc. There were a couple of odd olds applications that used them -- likely a cutlass with a 260 or some other models.
Since all olds dists have the same base they will fit in any olds including the GMC. A dual port came from a junk yard dog, not a GMC.
The port closest to the dist base (call it A) will pull in 12 degrees of vac advance (perfect for a GMC app). The other port (call it B) closest to the rubber tube fitting will retard or pull out 8 degrees. If someone is in love with that unit and wants to use it on their GMC, use port A hooked up to the carb "ported' stub. Leave the other one (B) open.
regards, dick
This is my comment. Please note that he says to use PORTED vacuum for the distributor vacuum source. NOT manifold vacuum. Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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