429 Rochester 4jet Question

CaddyCrosley

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Howdy folks,

I recently picked up a '65 CDV. She runs like a dream, no ticking, no smoke. However, on a cold start, it takes a snort of ether to motivate it to pop off, I don't believe the choke is closing. I have shop manuals on the way, hopefully arriving today, but I was wondering if anyone on here knew how that choke system operates and what my likely culprit is? Thanks!


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Caddylackn

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I am assuming this is a Rochester 4jet and not a Carter.

There is a coil spring in the round choke housing on the passenger side that contracts and rotates when it is cold and goes back when its warmer. That spring rotates the choke flap normally. There may be a metal line coming off the Exhaust passage on the intake manifold that goes to the choke spring housing to warm it. Sometimes this metal line rusts, breaks off, or gets blocked with carbon, then it never warms up the choke spring and never takes off the choke if its really cold. So, somebody may have manually adjusted the choke to stay off to compensate after they were driving around with the choke stuck on and were getting 7 mpg. Loosen the three screws on the round choke spring housing and rotate it to see if the choke closes or opens. I think rotating counter clock wise adds more choke. If there is binding in the linkage the spring may be unable to close the choke when its cold. If it is stiff or corroded take it apart and clean it. Rotate the assembly so the choke flap is closed (have somebody or prop the throttle linkage on part throttle) then turn the housing a little more so there is a little tension on the flap. Do this when its cold outside. Then tighten the three screws and see if its starts. Then if it starts, see if it turns off the choke when the engine is warm.

Best thing to do if the metal exhaust tube is gone or bad is retrofit an electric choke spring assembly in there and run 12V to it so your choke comes on when the ignition is turned on. Or you can go to a full manual choke retrofit. In '67 they went to a quadrajet and a different manifold with the quadrajet spread bores in the manifold. The Quadrajet is a much better carb than the 4 jet and I recommend using this instead if you can find one off a '67 caddy. Or you can just go to an electric choke Edelbrock carb like everyone else does. A 600 cfm 1406 would work.
 

PSYKO_Inc

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What vehicle(s) do you drive?
66 Cadillac Miller-Meteor Duplex
I believe that the 65 would have come with a Carter AFB, but I might be mistaken. One thing to check out is the thermostatic flap in the passenger side exhaust manifold. It has a butterfly that closes at low temp, forcing exhaust back into the head and up through a passage in the intake to warm the carb, and back out through the drivers side head and exhaust manifold. If that flap is stuck open, the engine will be sluggish until it warms up. If it's stuck closed, it will vapor lock, backfire, and have lots of drivability issues.
 

CaddyCrosley

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Yes, it indeed has the 4jet - don't know why I didn't attach a photo of it as well. Thanks Caddylackn, I'll look into the choke spring, see what I can find. As you can tell, it does have the tube running from the choke spring housing to the manifold, if I can do so without shearing it off at the nuts, I'll pull that line off and blow it clear with brake cleaner. I'd need an adapter plate to bolt a Qjet to this manifold, correct?

P.S. don't mind the cobwebs, I took this when I first bought the car, it's since been pretty well detailed and cleaned up in the engine compartment

 

PSYKO_Inc

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What vehicle(s) do you drive?
66 Cadillac Miller-Meteor Duplex
Yep that's definitely a Rochester carb. Q-jet has the same bolt pattern, but would would need an adapter to fit due to the huge secondaries not having room to open. An Edelbrock carb is also an easy swap, but needs a 1/2" spacer for the throttle blades to clear the intake. I had a 750 cfm Edelbrock carb on my 66 429 that the previous owner had installed. He said that it was a good improvement over stock, but I never got to experience it first hand (car had been sitting for years when I bought it and the carb was all gunked up, then it froze and cracked the block before I had a chance to get it running properly...)
 

Caddylackn

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yes, to run a quadrajet you would need a spreadbore adapter or an intake manifold from a '67 Cadillac with the 429. You would also want to use a Quadrajet of around the same size engine so the fuel metering and jets are close. So, best case would be to get an intake and carburetor from a '67 or better to get one from a Cadillac with the 425. The 77-79 Quadrajets are about the best performance Quadrajet carb to start with. You also want the quadrajet with the front fuel inlet if you can't find a '67. The Chevys had the side inlet so if you do get one of those try to snag the metal fuel line with it to swap.

In that year range, some came Caddys with 4 jets and some came with the Carter. The Rochester 4jet is easy to rebuild if you just want to run that.
 

CaddyCrosley

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yes, to run a quadrajet you would need a spreadbore adapter or an intake manifold from a '67 Cadillac with the 429. You would also want to use a Quadrajet of around the same size engine so the fuel metering and jets are close. So, best case would be to get an intake and carburetor from a '67 or better to get one from a Cadillac with the 425. The 77-79 Quadrajets are about the best performance Quadrajet carb to start with. You also want the quadrajet with the front fuel inlet if you can't find a '67. The Chevys had the side inlet so if you do get one of those try to snag the metal fuel line with it to swap.

In that year range, some came Caddys with 4 jets and some came with the Carter. The Rochester 4jet is easy to rebuild if you just want to run that.

Thanks fellas for the info! Qjet would get a little better fuel economy while cruising and in town, wouldn't it? I might try to see if I can get my hands on a 77-79 Qjet.
 

Caddylackn

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The quadrajet will get you better fuel economy at part throttle cruising due to better mixing and optimal fuel/air ratios. You can also optimize the vacuum advance curve. The quadrajet will also give you more power and better fuel mixing.

On these big ole' boats the key to manageable fuel economy is getting rid of all the parasitic loss:
1. Tire pressure- be fanatic on keeping these at optimal. Down 10 psi in a few tires = down a couple of mpg
2. Check all four wheels for brake drag and bad wheel bearings, bad seals. Take a short drive and use your hand. Anything that is dragging will be hotter than the other components, leaky wheel cylinders, or rear axle seals drip brake fluid or gear oil, it mixes with brake dust and creates a lot of drag inside the drum until it cleans itself out. Adjust rear drums so the parking brake is not creating drag unless it is pushed on.
3. Check water pump and alternator for bad bearings. Check to make sure fan belts are not too tight, create drag on putting extra pressure on the bearings.
4. If yours has a two piece driveshaft check the center carrier bearing, these are known to create a lot of drag when the bearing goes. You will notice a slight vibration, normally when these start to go. The bearing will be hot and noisy if its going.
5. Upgrade the ignition, coil, and wires to modern good components, new properly gapped sparkplugs. This is worth at least 1 mpg and better starting and running.

Your car's fuel economy was probably 14/11 when it was new running on 100 octane, so don't expect much more than this. Yours being old, 12/10 sounds reasonable if stock, running good, and decent compression all around. We don't have good enough fuel anymore to really advance the timing to get the max. power. The quadrajet should let you get at least another 1 mpg cruising, so I would say 14 -15 mpg could be possible at 60 mph if everything is running right. The best I have ever done with a 429 is 14 mpg in my '64 at 65-70 mph, which had the 429 and the jetaway transmission and a MSD blaster coil, aftermarket wires, and petronix ignition. I have gotten over 15 mpg in my '61 Fleetwood but I was driving only 50 - 60 mph in the winter with snowy roads. I probably had 500 lbs of motorcycle and parts in the trunk. That car has a 390 engine and 2.93 gears so it was probably at 2,000 rpms or under the whole way.
 
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