Help need new carb for stock 383 Magnum

Fuel and Air Systems

  1. dppayton

    dppayton Active Member

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    I have a stock 1968 RR, engine is stock including manifolds. I would like to change out the carb to a new one and have the old one rebuilt and saved for later. What carb is best for my setup and will fit my stock manifold and air cleaner?

    I have been looking at a Holley 670 Street Avenger but do not know if it would work.

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  2. Blacktop Voodoo

    Blacktop Voodoo Active Member

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    I am running a Holley 750 dual feed on mine. It runs excellent. I wouldn't go any bigger.
     
  3. Russ69Runner

    Russ69Runner Well-Known Member

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    That sound's rite. Any bigger and get wash down due to much un burnt fuel in the cylinder. Hard on the ring's also. Good luck.
     
  4. ‘69_Sunfire_RR

    ‘69_Sunfire_RR Active Member

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    Sorry I realize this is an old thread. I am running a 670 Street Avenger Holley that I bought a year ago. Basically bought a brand new carb from a guy who decided to go bigger after buying a crate engine with this carb delivered with the crate engine. Admittedly I did not know a lot about Holley’s at the time, but I was told by this person it was a 750. Not so. After learning much much more about Holley’s, it’s a Street Avenger 670. I have a ‘near stock 383 in my ‘69. Stock heads, valves, stock HP exhaust manifolds. I recently installed the stock grind, Mopar cam (.450/.464). I also installed matching Mopar springs. I am using the Edelbrock performer 383 manifold, not the RPM air-gap. Long story short I’m not too happy with the 670. I cannot seem to tune it well with this engine. I have a lean miss up around 3000 RPM but if I run the fuel mixture screws out much, she bogs at lower RPM. My car is a 4-speed. So I’m thinking of going to a true double pumper, dual metering blocks and dual accelerator pumps with mechanical secondaries. I also plan to go to a larger lift cam, closer to .500, RPM intake, and full length headers. Obviously the double pumper may not serve you well if you are running an automatic but I’d say consider a 750 with vacuum secondaries for your stock 383. Tuned right it should run well. I realize you could have used this information a couple of months ago! Sorry I missed this post!
     
  5. 69hemibeep

    69hemibeep Sponge Bob Square Wheels

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    670 should run pretty good on your combo, it just needs tuned by a pro. The mixture screws are for idle only!
     
  6. ‘69_Sunfire_RR

    ‘69_Sunfire_RR Active Member

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    Ha, yes a pro I am not. Motivated novice for sure. I’ve tuned the carb and timing with a vacuum gauge etc. I’m running about 18 degrees initial and around 36 total. At that I’m pulling about 25 inches of vacuum which seems pretty good. Tuning the carb at idle I’m about as lean as I can be which may be the issue. I’m about 1.5 turns backed out from the idle mixture screws being fully seated/tightened. I understand this is really the starting point on the idle mixture tuning, but I achieve the best vacuum here. Thinking of backing them out another turn or two to see how the car performs. I may go to different jets as well. Anyone recommend a specific jet size? How about nozzles? I’m also not sure what spring is used in the vacuum secondary pot, I may change this also. Also, how streetable are the mechanical secondary Holley’s with a 4-speed? I don’t expect it would be too much for my config but wondering everyone’s experience with mech secondary carbs. Thank you all!
     
  7. Russ69Runner

    Russ69Runner Well-Known Member

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    I would start with quarter turns on the needle jet. It is rough using this new fuel in old carb's. Try summit racing help line or tech. If you call Holley they can set you up with what you need. Have run double pumpers in the past but that was for racing. Used a lot of 650 Holley's and Edelbrock carbs. Lean towards the Holley's. Easy to rebuild and the jet sizes are in many ranges. So I called about mine and it had nitrate floats in it. It would flood also stall. It ended up being the floats where to heavy with the float contaminated with fuel. New floats and it ran like a charm. Good luck with it match the carb to the motor size.
     
  8. ‘69_Sunfire_RR

    ‘69_Sunfire_RR Active Member

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    Thank you Russ, all great advice! I ordered a few jet sizes and a few nozzle sizes. Also bought a spring kit for the secondary pot. Going to spend the weekend tuning. I’ll let you all know what happens. Choosing by the size of engine is a little tricky but based on some of the calculations I’ve done vs. this build, around a 700 cfm carb is what I’m looking at. I guess I’m close enough. I’ll jet it up a few sizes and add a larger nozzle to see what happens. I’ve read that this wakes up the 670 holly pretty well. My car runs pretty strong, lays rubber going from 1-2 and chirps going 2-3... 275-15’s. I’m not too concerned I just feel a hesitation sometimes, kinda feels like a lean miss. -Jeremy
     
  9. 69hemibeep

    69hemibeep Sponge Bob Square Wheels

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    You dont even know what power valve is in it. Do you know how to select a power valve? Your going to throw parts at it, get upset and buy a new one that neeeds tuned to your engine.
     
  10. ‘69_Sunfire_RR

    ‘69_Sunfire_RR Active Member

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    I actually do, it’s the 6.5. You’re correct, I don’t know how to select a power valve. I’d appreciate any advice here. Thank you!
     
  11. droptop

    droptop Well-Known Member

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    Why not just rebuild the original AVS and put it back on? It works very well for a “stock” 383. It was good enough for Chrysler engineers.
     
  12. 69hemibeep

    69hemibeep Sponge Bob Square Wheels

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    How to ensure your Holley carburetor is using the right power valve for your engine. Holley carburetors have a power enrichment system that provides fuel to the main power circuit during heavy loads or under full throttle situations. The vacuum operated power enrichment system is controlled by a Power Valve that times the operation to your engine's specific needs.

    How it works:
    The power valve opens at low vacuum, such as at wide open throttle, and directs more fuel into the main power circuit. The valve itself is a small rubber diaphragm with a small coil spring. When opened, it allows fuel to flow through a calibrated opening in the metering block called the power valve channel restrictor. This restrictor determines the amount of additional fuel delivered to the engine.

    Problems:

    The incorrect size power valve, or a blown out power valve can cause problems such as poor fuel economy, black smoke emanating from your exhaust, dark or fouling spark plugs and a poor idle. If you suspect that your carburetor has a blown-out power valve, you can perform this simple test.

    1) Check the manufacture date of your Holley carb.

    Performance Holley carburetors come with a power valve blow-out check valve built in. It prevents damage to the power valve in case of backfire. Holley carbs older than 1992, however, may not have this check valve built in.

    2) Test it using the idle mixture screws

    If you still suspect the power valve is blown out, start your engine and allow it to idle and get to normal operating temperature. Then, turn the idle mixture screws all the way in. If the engine dies the power valve is not blown.

    High Performance Engine Power Valve Selection:
    High performance engines with modified cylinder heads, long duration camshafts and single plane intake manifolds may require a change to the power valve. To find out which power valve your high-performance engine needs, you can perform the following procedure:

    1) Hook a vacuum gauge to an intake manifold vacuum port.


    2) Warm up the engine and note the vacuum reading at idle. Automatic transmission vehicles need to be in the Drive position, while manual transmission vehicles can be in Neutral.


    3) Divide the vacuum reading in half. The number will determine the correct power valve.


    Each power valve is stamped with a number that indicates the correct vacuum opening point. For example a power valve with the number #65 stamped on it, will open at 6.5 inches of engine vacuum. As an example, a vacuum reading at idle of 13-inches, is divided by two and results in a 6.5 inches of vacuum. Therefore, you should have a #65 Holley Power Valve installed in the carburetor.


    If you divide the vacuum reading and it falls on an even number, you should select he next lowest power valve number. For example a vacuum reading of 8-inches, divided by 2 and you come up with a number of 4. In this case you would use a #35 power valve.

    Finally, if your engine produces 13 inches of vacuum or more, the stock power valve that the carburetor is equipped with from the factory, is sufficient.
     
    CombatMedic80 likes this.
  13. Roadcuda

    Roadcuda Well-Known Member

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    I agree with Harold. My car has a stock 383 with the original Carter, 4682 carb and the car runs very well with it.
     
  14. HD539

    HD539 Well-Known Member

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    I second (third?) the statement regarding the Carter carburetors. I also run the carter 4682 on my 383. I recently rebuilt it and am very happy with the result.
     

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