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312 carburetor choice

Posted By scottlboyd 6 Years Ago
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scottlboyd
Posted 6 Years Ago
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Hi all. I have a stock 57 Ford 312 engine bore .060 over when it was rebuilt and have been running a Holley list 1849 with mixed results.
I believe this is a 550 cfm carb. I experience idle issues, poor low end performance which leads me to believe that I might have
too much carb. Before I rebuild it, I am considering a brand new Holley 4160/ 0-8007 which is 390 cfm. Research shows that
list 1273 Holley came stock with the engine and was rated at 410 cfm. Engine is 322 cubic inches bored out and is stock in 
every other way (auto trans). The Holley carb selector points to the 390 carb to be the one to use. Any help that you can give
me to make a decision would be most helpful. I don't want to choose a carb that is too small either.

Scott

Redding, California
charliemccraney
Posted 6 Years Ago
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Is the carburetor known to be in good condition or is the history unknown and it possibly needs a rebuild?
Have you spent time tuning or are you running it in the "out-of-the-box" configuration?

In general, something around 500cfm is a good compromise for a stock engine.  550 is more than it needs but possibly is not too big since it has vacuum secondaries.


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scottlboyd
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thanks for the reply! The carb I have in there now is of questionable origin-in other words, a friend who had supposedly rebuilt it told me it would work well on my engine. If I keep it, I need to have someone rebuild it properly and tune it properly-neither of which I am capable of doing. That is why I was looking at getting a brand new carb as a good starting place. Holley also makes a list 1848 brand new which is 465 cfm but I believe it has scrubrolet linkage and would have to be adapted for the Ford linkage. My car is almost always on the lower rpm scale-never raced or revved high. Do you think the 390 cfm carb is too small?

thanks for the help

Scott

Redding, California
NoShortcuts
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scottlboyd.  I would not rush to purchase a replacement carburetor.  The vacuum secondaries on the Holley carb you have will adjust for the cfm you need for how you drive your 'Bird.

I would not expect to be able to take any new or used carburetor out-of-the-box or off the workbench, install it, and not need to do some sorting out of how it is set-up to assure optimum performance.

I would recommend that you connect with someone who knows Holley carbs and is GooD at pursuing vehicle drive-ability issues.

Hope this helps.   Smile  


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scottlboyd
Posted 6 Years Ago
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Thanks for the reply! I have located such a person near me and will consult with him before I make any rash decisions-good advice.

Scott




Scott

Redding, California
Talkwrench
Posted 6 Years Ago
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Auto ?   Sounds like you just have a crap carb , Y's are pretty forgiving, Ive tried a 600 Holley , 450 Holley and a 1406 600 Eddie [on there now] and Vac secondaries, lots of adjustments made and I have to say there's not much between any of them ...

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skipLYB
Posted 6 Years Ago
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Pick up a copy of HP books Holley Carburetors, Intake Manifolds, & FI and or Haynes Holley Carburetor Handbook, I have both great info on setting up carbs especially idle, off idle & cruise which sounds like your carb. I've never seen a bad carb but have seen a lot of miss-tuned carbs by folks who don't know how a carb works! I've spent my time in that line! All carbs are an amazing engineering feat, they aren't simple and everything does something to contribute to drivability, power, and economy. The trick is get it all working together!! If you don't understand the details you never will.
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Scott.  Don't be surprised if the technician who works on your car indicates that he needs to do a full check-up of your engine other calibrations or operating condition before putting your carburetor under scrutiny.

While your engine's operating problem may be related to the carburetor you're running, there are many other 'things' that may instead be the root OR otherwise contribute to the problem.  Generally, the carburetor is the last 'thing' to adjust after virtually everything else has been verified as being properly calibrated or operating. Ruling these other potential contributors out first, is the usual order before suspecting the carburetor or setting out to 'fix it'.

Your technician may begin with an engine vacuum gauge test done at normal engine operating temperature.  Depending upon what that testing shows, the tech. may desire to do a compression leak-down test.  He may also do an ignition system operating test with an oscilloscope.  This may lead to work related to spark plug and / or spark plug wire replacement.  After checking the ignition point dwell setting and the existing ignition timing setting, he may, IF equipped to do so, pull your ignition distributor to check the centrifugal advance curve and to assure proper vacuum advance operation on a distributor machine.  The checking of the distributor advance curves can be accomplished with the distributor installed on the vehicle's engine, but a distributor machine is preferred if he still has one.  If previously removed, after reinstalling the distributor, he may check the engine valve lash setting.  Subsequently, he'll check your ignition timing setting at idle (with the vacuum line to the distributor disconnected and taped closed) and then will check the idle adjustment of the carburetor.  After doing all of this other 'stuff', he may have you take him for a road test involving low speed operation, stop-and-go operation, engine operation in going up a long hill, acceleration to attain highway driving speed, performance when doing the equivalent of a vehicle pass at highway speed, and performance at consistent highway speed for a reasonable distance.

Your technician may do some other things, but the above narrative will give you an idea of what was common to do with pre-computer controlled engines that had carburetors, solid lifters, and ignition distributors with ignition points.   Hehe 

Hope this helps!  Smile


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scottlboyd
Posted 6 Years Ago
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Very good, solid advice and I thank you for it. I will follow your recommendations and get the car into my tech guy and have him narrow the problem down before I go out and spend a lot of bucks on something that really isn't a problem (like I have done before). I appreciate your taking time to help me!

Scott

Scott

Redding, California
Florida_Phil
Posted 6 Years Ago
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I bought a new Holley 1848-1 465 CFM and couldn't be happier with it.   My motor is a .040 over 292 with 1957 G heads, iron intake and distributor.  I have no flat spots and it idles smooth as glass.  The secondaries open when they are supposed to.  Installed it right out of the box with no mods.  You'll love it.


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