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Radmo1 · 07-08-2018, 06:26 PM

I've owned this car since 1980. It's a California TA. with Calif. carb. Very stock automatic car. 2nd owner. Ran fine until recently when idle dropped to about 300 rpms at stop lights, stop signs, yield signs etc. Now when it starts, RPMs go up to 1000 to 1200 and then drops to zero and car dies. Had the carb rebuilt but no change. If I keep the RPMs up to around 1000, until it warms up, it's drivable. Presently, I have the hose from the Vacuum Advance and the Transmission Module connected to a port at the top stack of the carb and brake booster routed to back of carb at the base. Anyone out there had this problem? Radmo 1

Formulabruce · 07-08-2018, 11:42 PM

Drivers side , just above the Idle mixture screw is the PORTED Vacuum that the Advance plugs into. This works "just off idle"
Another issue is that your base probably needs the idle mixture circuit drilled out for this fuel. You probably have a clog of dried out fuel in the idle circuit.
On a Rebuild, the Idle circuit needs to be addressed, especially with no APT on your carb.
Good luck!
PS, getting a 77-79 Pontiac Carb rebuilt Cliffs way, will make driveability Great! Shelf the original then if you do not want it modified .

1971455HO · 07-09-2018, 01:16 AM

[QUOTE=
PS, getting a 77-79 Pontiac Carb rebuilt Cliffs way, will make drive-ability Great! Shelf the original then if you do not want it modified .[/QUOTE]

I'm sure it would run great Bruce, but, will the mounted automatic choke on 73 & up fit up under his '70 T/A breather base? I was thinking it wouldn't.

Formulabruce · 07-09-2018, 01:25 AM

Quote:

Originally Posted by 1971455HO

I'm sure it would run great Bruce, but, will the mounted automatic choke on 73 & up fit up under his '70 T/A breather base? I was thinking it wouldn't.

use the divorced choke, why change that?

Formulabruce · 07-09-2018, 01:27 AM

If you like driveability and plan to actually use a 1970 Pontiac, its well worth the effort

77 Canamman · 07-09-2018, 07:17 AM

Did the rebuilder pull the idle tubes and super clean the passages? I have been doing that on all of my refreshes, and you would be suprised the amount of junk you'll find when the tunes are pulled. Also the tube size can be changed if necessary for better idle fuel supply.

Radmo1 · 07-09-2018, 10:34 AM

Quote:

Originally Posted by Formulabruce

Drivers side , just above the Idle mixture screw is the PORTED Vacuum that the Advance plugs into. This works "just off idle"
Another issue is that your base probably needs the idle mixture circuit drilled out for this fuel. You probably have a clog of dried out fuel in the idle circuit.
On a Rebuild, the Idle circuit needs to be addressed, especially with no APT on your carb.
Good luck!
PS, getting a 77-79 Pontiac Carb rebuilt Cliffs way, will make driveability Great! Shelf the original then if you do not want it modified .

Very new to this site Hopefully this will get to you this time. No port on drivers side middle stack, so Vacuum Advance and Trans Module hoses are connected to port on passenger side middle stack. Only other port is on bottom stack slightly to drivers side. Hose to canister is plugged in there. Carb just been rebuilt by local rebuilder I have used for a while but he has not helped. Is there a way to email a pic of carb to you? Jay

Greg Reid · 07-09-2018, 11:09 AM

The vacuum hoses may very well be in the wrong place (and it kinda sounds like it) but if they are where they've been all along, I'd say that for right now at least, it's a secondary issue. Something obviously changed.
Maybe a vacuum leak? Old, dry rotted vacuum hoses?
Hard to find anyone nowadays, even pro mechs, that know what they are doing when it comes to Quadrajets or even carbs in general.

johnta1 · 07-09-2018, 11:58 AM

If this just started after running OK, I'd 1st see if the carb is wet when it happens.
Take air cleaner lid off and look and see what it looks like in there.
(choke position, wet, dry, etc)

Does it start up after it dies?

Runs only when giving it more RPM?

I would take the top of carb off and see what the fuel level looks like when it happens.
Possibly not enough fuel or too much fuel.

Also take a vacuum reading and see what it shows.

Toooooo many things to look for to give a good idea of what is wrong.

Formulajones · 07-09-2018, 02:11 PM

There is no "ported" vacuum source on the 70 carb, if the correct carb is being used. Mine is also a RAIII Van Nuys built with evap system. No ported vacuum source on my carb.

Radmo1 · 07-10-2018, 10:03 AM

Quote:

Originally Posted by Formulajones

There is no "ported" vacuum source on the 70 carb, if the correct carb is being used. Mine is also a RAIII Van Nuys built with evap system. No ported vacuum source on my carb.

The number on my carb is 7040570. Same as yours? Jay

Radmo1 · 07-10-2018, 10:04 AM

The number on my carb is 7040570. Same as yours? Jay

Formulabruce · 07-10-2018, 12:33 PM

If it uses a Vacuum advance, it gets ported vacuum from somewhere. Could be in California it it a switched vacuum. The advance is there to keep car from stalling at a stop as car slow. Have to look at my carb again ...

1971455HO · 07-10-2018, 02:33 PM

Quote:

Originally Posted by Formulabruce

use the divorced choke, why change that?

Thanks Bruce, I'm a dingbat, it didn't even occur to me that you could just remove the hot air choke and install your own divorced choke stuff. Duh!

If there's no other hurdles to deal with, I'm thinking, I might contact Cliff and do the same thing.

Just didn't want to modify my breather base.

unruhjonny · 03:10 PM

I seem to recall that 1970-1972 distributor vaccum hose routing was all done very much the same way;
I did a search and found these:
1970 picture 01

1970 picture 02

1971 all except 455HO

I do believe that the front of the carb could have a ported vacuum source - some carbs were not manufactured with this port, but during a generic rebuild, many which didn't have these ports, had them added;
This front port is the one which I am speaking of:

I do also believe that if a port was present or added to the right, and above the fuel inlet (pictured below), that was ported vacuum....

IIRC it has something to do with where the vacuum is taken from - above, or below the butterflies.

Formulajones · 07-10-2018, 05:29 PM

That one up top, even though it's above the base plate, it's full time vacuum. That's where the transmission vacuum modulator hooks up.

unruhjonny · 07-10-2018, 05:59 PM

/\ ok, thanks for the correction;
I knew that's where the transmission line hooks up, but didn't realize it was full time.

Formulabruce · 07-10-2018, 07:37 PM

Quote:

Originally Posted by Formulajones

There is no "ported" vacuum source on the 70 carb, if the correct carb is being used. Mine is also a RAIII Van Nuys built with evap system. No ported vacuum source on my carb.

EEC controlled, and TCS .It probably has Full vac at low temp, and switched at Idle, EPA hated the Vacuum advance, the one thing that could improve on engine efficiency..

Formulabruce · 07-10-2018, 07:41 PM

With enough built in advance when timing is set, no vacuum advance is really needed. Mine is disconnected and I run an automatic. Might be more important at 10.5:1 CR though

Formulajones · 07-10-2018, 11:32 PM

Quote:

Originally Posted by Formulabruce

EEC controlled, and TCS .It probably has Full vac at low temp, and switched at Idle, EPA hated the Vacuum advance, the one thing that could improve on engine efficiency..

Yeah, when I smogged it in California they would unplug the vacuum advance, and even put a warning sticker on the inner fender to leave it unplugged. I'd plug it back in as soon as I left the lot, lol.

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