A Closer Look at the Carb Setup with Questions
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The linkage all seems to work. What exactly is presumably on backwards? This looks like the setup from the service manual, unless I missed something.[/QUOTE]
My FSM shows it the way yours is. It works either way. Its the adjustment that's counts.
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My '68 GTX with the original Hemi and carbs was set up by a previous owner who rebuilt Hemi carbs professionally, Dick Katter, in Woodbridge, Va. He bypassed the port on the back of the manifold as well, and replaced the factory choke with a manual valve. He owned the car for 31 years, and while not concours correct, it drives beautifully.
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CORRECT....the purpose is to INCREASE the distributor vacuum to maximum degrees, when DECELERATING, to improve emissions by providing more advance during lean coast down then, after a programmed delay, return to normal. Since the vacuum advance port connection is on the REAR carb, it should be connected there not to the front carb. IMO...the carb linkage is backward but as long as it works, should be OK Pethaps consider a 1971 HEMI choke control system (manual cable operated) in lieu of a hot air choke assrmbly, if not concurs restoration..... just talking out loud....
BOB RENTON
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The vacuum control is for both Auto and 4 speed hemi, the larger port and closest to the spring(rear) goes to Manifold vacuum. The plastic small port on yours (points forward) goes to the rear carb ported vacuum. The other side port which is closer to the front of the valve goes to your distributor. Normally there is a nipple fitting on the manifold that is used as the source for manifold vacuum on the valve. Even if not using it you should run with carb ported vacuum to the distributor.
The valve basically is measuring between manifold vacuum and ported vacuum and using what is higher.
The coupling rod does go slot to rear carb but either way works. Rear carb does all the low to mid range stuff so no need to be moving the rod until you actually want it to open the forward carb blades. Only one adjustment as the progressive rate is built into the levers. Set it so that front carb is fully open when rear carb is.
As far as choke, you would need the heat tubes, manifold valve, and you have to go back into the rear carb and remove the plug or drill it to the correct orifice size for your set up. The rod is common for the 66-69 carbs. The 70-71 used a unique and different one. So the idea if an electric choke is a good one if you don't have all the exhaust tubes for it.
The valve basically is measuring between manifold vacuum and ported vacuum and using what is higher.
The coupling rod does go slot to rear carb but either way works. Rear carb does all the low to mid range stuff so no need to be moving the rod until you actually want it to open the forward carb blades. Only one adjustment as the progressive rate is built into the levers. Set it so that front carb is fully open when rear carb is.
As far as choke, you would need the heat tubes, manifold valve, and you have to go back into the rear carb and remove the plug or drill it to the correct orifice size for your set up. The rod is common for the 66-69 carbs. The 70-71 used a unique and different one. So the idea if an electric choke is a good one if you don't have all the exhaust tubes for it.
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I’ll add an assumption from my car - the stock choke functions OK on my car. It closes and brings the fast idle into play on a cold start and the choke will open fully after it runs awhile. But I think the whole operation of the choke tubes and intake pipes was designed around a functioning heat riser valve that would restrict exhaust flow in the right manifold and direct exhaust gasses & heat to the choke and manifold. Without a functioning heat riser it doesn’t quite flow and work as well as designed - although at least for my garaged example it functions adequately - just don’t set the choke too rich. How many of us run an operating heat riser anymore? For that reason an electric choke wired to the input side of the ballast resister probably makes sense.
Just my 2 cents and rambling thoughts.
Just my 2 cents and rambling thoughts.
Dragon Slayer
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Mine is connected and works. I did edit my post above, the Vacuum control was on Auto and 4 speed for the hemi, other cars just 4 Speed. The 4 speeds should have a dashpot on the rear carb for 68-69.
Refreshed on cap. 66-67 cap was CA only, Hemi exempt in 66. 68 onward all state was cap. The Cap distributor valve only activated in one way. When Intake vacuum was great and capable of overcoming spring; and carburetor vacuum low.
That case is a deacceleration with throttle closed but rear wheels coupled to motor still at high rpm. That creates a very strong motor vacuum, and lean condition. Dash pot helps by not letting throttle blades full close until dashpot pressure overcome (delay closing) and the vacuum valve advancing vacuum timing to start the ignition firing earlier to get a better burn and reduce emissions. Because a TQ does not efficiently drive the opposite( wheels turning motor vice motor turning wheels), the valve not needed on autos, though documentation said except hemi.
Refreshed on cap. 66-67 cap was CA only, Hemi exempt in 66. 68 onward all state was cap. The Cap distributor valve only activated in one way. When Intake vacuum was great and capable of overcoming spring; and carburetor vacuum low.
That case is a deacceleration with throttle closed but rear wheels coupled to motor still at high rpm. That creates a very strong motor vacuum, and lean condition. Dash pot helps by not letting throttle blades full close until dashpot pressure overcome (delay closing) and the vacuum valve advancing vacuum timing to start the ignition firing earlier to get a better burn and reduce emissions. Because a TQ does not efficiently drive the opposite( wheels turning motor vice motor turning wheels), the valve not needed on autos, though documentation said except hemi.
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Just so I am clear, I can technically bypass or disconnect the vacuum valve and run vacuum line direct from the rear carb to the distributor and be able to tune it just fine like that? The valve is obviously not set up currently to work at all. I don't even understand what kind of nonsense the previous owner had going on here. The possible port on the back of the manifold was obviously intentionally blocked.
I am also leaning towards an electric choke simply for ease of operation and set up. Also considering whether to do some type of electronic ignition setup. I don't want to go the MSD route. I just want something clean, neat, functional and not obviously hideous.
I am also leaning towards an electric choke simply for ease of operation and set up. Also considering whether to do some type of electronic ignition setup. I don't want to go the MSD route. I just want something clean, neat, functional and not obviously hideous.
Yes you can run without that valve. Just run the line from that rear carb port to the distributor.
Electric choke most likely is in your best interest.
Most common ignition would be the Mopar with an ecu. MSD has a ready to run distributor that is pretty basic to install. There are other options but the MSD would be my choice. Mancini has one that I have on my Hemi.
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IMO.....
WHY NOT just continue to utilize the origional Prestolite dual point distributor? It would look origional and provide functional and reliable ignition operation. As stated previously the engine will operate just fine without the vacuum advance valve connected. And an electric operated choke is a excellent alternative to the origional hot air choke and associated plumbing. Just my opinion of course.
BOB RENTON
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383man
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This is right. That emission valve just would advance the ign timing on hard decell by sending manifold vacuum to the vacuum advance on hard decell to help with emission's. As someone said most just dont use it but if your restoring a car back to 100% original then you will want to use it. For a driver car being restored myself I would chuck it but I am one who dont worry about my car being 100% stock since we always modded our muscle cars back in the day. Good luck to you as I know I have pics somewhere of the hoses but it would take me a long time to find it. Ron
Dragon Slayer
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You can find pictures from google. The vacuum tree was on the back of the manifold. A charger for example had the 3 output tree normally. Large to power booster, one to the vacuum can for Head lights, and the other as manifold input to the valve. The correct assembly line hemi valve I believe is the one shown with a metal front. Not plastic like the non hemi motors had. Bracket is correct and hemi only. Last pic also show hemi 4 speed dash pot.
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