Carb full throttle at start

GMC guy

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#1
Make
Pontiac
Model
Parisienne
Year
1968
Miles
40,000
Engine
350
68 pontiac with 350 auto. 350 Engine just installed from a 1983 chev truck. 40 k it has a carter afb 9400s 4 bbl carb. I start it and it wants to go full throttle and yet the throttle on carb is not touched. I have to turn key to off immediately to prevent engine from roaring. The choke is on. I held choke open and it seems like it is out of fuel and wont start. I pumped it once and could see the gas squirt into the carb. I need it to start and idle. what do i do to correct this carburetor?
 

billr

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#2
Sounds like you have a large vacuum leak somewhere. I assume you can see the throttle blades in the closed position when this happens.

I don't think it is a carb problem specifically. Do the carb ports match up with the manifold, no go-fast carb added that isn't stock? (GM didn't use Carter much/any back then; Rochester and Holley were the ones I remember seeing stock).
 

GMC guy

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#3
Yeah...the large port in the back is not connected to anything. And the previous owner of this engine said this carb worked well for him. Guess ill find a line and run it to the power brake. Thank you.
 

billr

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#5
Isn't a '68 Parisienne rather hard to stop without the power-brake in operation???
 

nickb2

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#6
Ha, I was kind of asking myself that.
Isn't a '68 Parisienne rather hard to stop without the power-brake in operation???
I had an old pontiac lemans 1971, and it was all drum brakes. I remember seeing a few 68's in the parisienne models also had drums. But it did not have a carter carb. It was a roch. But I did go on the net a bit, seeing carter in the parisienne's in 68 but only for 2bbl. In the big blocks. I think they stop using carters in 69.

But I was born is 75, so what do I know about this era? Not much. When I was apprenticing, I saw a few, but they all had the big blocks. They were confusing back then because they both called themselves the 4MV. I think some of the gaskets and seal were interchangeable.

Last time I touched a carb was a few months ago. That was on a yamaha bike. Before that, maybe 15yrs ago. I see plenty for the big block carb on the net, but nothing for the 350/5.7l.


Not my writing, and since I live in canada, this may not apply to you.

Carter introduced the AVS in 1966. Chevrolet used it on the 275 horsepower 327. The acronym AVS meant “air valve secondary”. Basically, the first incarnation of the AVS was an attempt to place the “demand” spring tension secondary on the square-bore AFB style carburetor. From a manufacturing standpoint, much less expensive to produce the spring tension secondary than the weighted airvalve. Chevrolet used it one year, but then dropped the AVS in favor of the Rochester Quadrajet. Carter still thought it could work, and during 1967 did lots of R & D on the primary circuit, utilizing the 3 step step-up rods and some differences in the primary venturi cluster (remember the Clean Air Act of 1966, to take effect with the 1968 model year had just passed). Due to the really precise lower RPM metering characteristics on the revised AVS carburetor (useful for smog emission calibrations), Chrysler purchased them for use beginning with the 1968 model year. These carburetors were quite troublesome, and before the final demise of the AVS after the 1971 model year, the AVS sometimes didn’t last as long on a new muscle car as the first tank of gasoline! Most enthusiasts changed them out, either for pre-smog AFB units or for Holleys. Carter did make one final attempt to market the AVS in 1972, as they offered several aftermarket versions. However, these didn’t sell; if fact, I have never seen one!
 
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nickb2

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#7
Basically, what I think bill and I are trying to say, is that maybe this is not the right carb for that year. Again, I am saying maybe.

Cuz I see tons of rochester for 68, no carter at all. I think from what I garter, they stop making carter AFB`s in 67 for pontiac. This may be a chevrolet engine in there.

Screenshot (1).png Screenshot (2).png
 
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PC

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Fairly recently I had a 1971 LeMans 350 2 bbl. with manual drum brakes, first few highway stops were fine, after that, cross your fingers it stops. Had the throttle on a big block Chevy stick open, had to kick in the clutch and kill the key. A large vacuum leak from the booster port would cause it to die with a properly functioning carb as the fuel metering is fairly constant at idle. Fuel injection will try to compensate for the extra air by adding fuel boosting RPMs.
My thinking here is once the motor lights, engine vacuum is pulling the secondaries open for some reason. Might want to get a exploded diagram of that carb and see if a link or some sort of return spring is missing on the secondaries. I'm sure someone here can dig up a diagram of that carb. Could even be a port on the carb. connected to manifold vacuum. Don't recall what the Rochester Quadrajet used to close the secondary plates. Guys used to put a screw in the link on vacuum secondary Holleys to imitate mechanical secondaries, but w/o the accelerator pump on the secondaries, it created a nice bog when mashing the pedal.
 

nickb2

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#10
"PC, I will try to take a pic of my old 71 mans.

It was bronze, just like paul newmans car in that hockey flick back from the 80`s or 70`s. Slapshot was the name.

 

nickb2

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#11
I don`t have the 71 anymore, it was sold off to pay for my sons difficulties.

But I think when my GF gets here, we can take a pic of a pic.

I sure enjoyed that car. I was 19 and loved the outdoor cinemas. I used to bring a different GF every weekend to keep the boys off balance.

That way they would`t know what rear end I pulled or if I was roller. The particular setup I had was canadian only. It came as a 6 inline 250 with a 2bbl carter. But the bonus with this setup is you got the power glide two speed. Very sought after quarter mile auto trans. So that endend up with a direct drive

NASCAR puck rear end. That power glyde powered through two torque limiters. Stalling @ 3.5grand was scary for thew mechanics of it.
 
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PC

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Nickb2, had that 71 LeMans up till 7 years ago, drove it every day, was reliable as a locomotive, never failed to start. Rebuilt that 2 bbl Rochester, parts man commented he hasn't seen a carburetor float in years. Oh well. That Pontiac was a nice sleeper as that 4 door boat surprised a few people not realizing those Pontiac motors make tons of torque. We had one nasty winter, snow and ice half way up the door, threw the chains on, warmed it up a bit and pulled right out. I miss that LeMans.
 

nickb2

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#13
Here is pic I said I would take of a pic. Man, I had hair back then!! That thing was a tank. I liked the two door version better than the four door but in essence, they made same torque etc stock. I think they called this lemans model the "T"37. I think the "T" model was the four door and two door but with the in line 6 version. When I bought it, it had no side lettering. When I was done with it it had a 350 with a direct drive for the front. It was a kit given to me by an old mentor of mine.

This was the day I bought it off some lady who said her great aunt left it to her in her will. She didn't like the big steering wheel and sloppy brakes. It was 4 drum after all. I bought it for 1000$ as is. Just like in the pictures. I don't have pics of when I cleared the mat base coat after I had layered down two black racing stripes from hood to rear bumper the same width as signature pontiac lemans/GTO split front grill.

Just look at that grin on my face. :cool:
20160102_003913[1].jpg 20160102_004535[1].jpg
 

nickb2

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#14
This was the first real muscle car I ever owned. The other one was a 84 GT mustang. If you look at the above pics above, you will notice all the lines lined up well. The front "nose" section that sagged on almost every car of this era was perfectly lined up. The heavy doors had no slop in the hinges and closed with a soft "thunk".

As I wrote before, many nights at the drive in theater fogging up those rear quater crank down windows. It came equipped with an AM only radio. Left it there and put in a cassette deck in the glove compartment to keep the stock look. Although the OEM speakers couldn't handle the power of the american bass amp. So in went 4 blaupunk's and two 12inch drivers for the baggage compartment. I sold it for 1600$, but kept the sound system. That went into many many other cars I owned. Man did I piss off the neighbors back then.:p The amp looked alot if not exactly like this one. https://picclick.com/Old-School-American-Bass-VFL-1000-2-channel-142661052034.html

I ended up leaving it my old 92 eagle talon cuz MP3's were then the new thing. Was time for a new F you setup.

Anyways, @ PC, thx for sharing. Fun to go back down memory lane sometimes.
 
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PC

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Funny, same here, AM radio and manual drum brakes. It did have power steering and A/C after flushing the system and replacing the compressor , not a drop of oil came out of the compressor. Found half a dozen receipts for A/C work, charge, etc, in the glove box. Put in a FM converter I had laying around and kept the speaker in the dash. WOW, you ran that amp off the stock 37 amp alternator? Actually those old Delco-Remy alternators were pretty robust, once changed the brushes on a straight 6, middle of winter w/o removing the whole alternator from the engine. Try that on a car today.
Only pictures I have were after some genius totaled it while parked on the street.
Wonder how this fellow is making out with that carburetor issue?