403 Dual Vacuum Advance (California Emissions)

T

tyhardiman

Member
May 22, 2017
42
3
8
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?
--
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
 
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
 
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 .

> 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:
> 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
 
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
 
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

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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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
 
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

>
> 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
>

>
> 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
>
> _______________________________________________
> 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
 
Ken,

I have a used one if you want it. I took it off of someone's distributor
years ago
and never got around to throwing it away.

Gary Kosier
77PB w/500Cad
Newark, Ohio

--------------------------------------------------
From: "Ken Burton"
Sent: Sunday, June 04, 2017 1:46 AM
To:
Subject: Re: [GMCnet] 403 Dual Vacuum Advance (California Emissions)

> 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
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
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

> 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
>
 
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.

> ​...
>
> 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
>
 
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.

> 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
http://www.appliedgmc.com
1-800-752-7502
 
> 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,

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 - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Still Loving OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Thanks all for the info. Some of you were so entertained by that 1977 California emissions diagram that I would be remiss if I didn't publish the 1978
diagram for your continued amusement:

http://www.gmcmhphotos.com/photos/dual-vacuum-distributor/p63298-1978-california-emissions-schematic.html

--
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
 
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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