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By Lex - 11 Years Ago
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I have a 57 Bird with a 312. It has one of the Holley 465 replacement carbs on it that's about 6 months old. This car has always had a lopey idle as if it had a small street cam in it. I had a guy at a car show this weekend told me his Dad's 57 idled smooth as a new car today. If you knew me, that got me working on the tune. It's rough enough at 800 RPM you can feel it in the steering wheel at stoplights. I always considered myself as pretty good on Holley carbs but I cant change the idle of this thing no matter what I do. The car runs great off idle. Question is, Was that guy just full of Shxx when he told me that? How smooth of an idle should I expect? I've never listened to another one run so I'm kind of shooting in the dark. Thanks!!
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By charliemccraney - 11 Years Ago
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If it is stock, it should be pretty smoothly and idle well below 800rpm. If it is rough at 800rpm, then it has some issue or it may have a bigger cam installed. If the idle won't drop, then you probably have a vacuum leak. Otherwise it would not get enough air to idle at 800rpm and vacuum leaks can also make it run rough.
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By Lex - 11 Years Ago
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Also this carb had the little lever on top of the fuel bowl that opens at idle. The former owner stripped the inlet threads and I put a fuel bowl on it that wasn't drilled for the vent so I left the lever off. Would that make a difference?
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By charliemccraney - 11 Years Ago
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I don't know what that is but certainly any deviation from stock can affect the carburetor and therefore the way the engine runs. That is something worth looking into.
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By Talkwrench - 11 Years Ago
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Manual or auto? Could be a vacuum leak as suggested . How advanced or retarded are you with your timing? . Start learning how to use a vacuum gauge, best tool you can have.
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By Riz - 11 Years Ago
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Found this a few years ago-not fully encompassing, but pretty handy
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By Lex - 11 Years Ago
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Already been the vacuum gauge route. It pulls about 18 inches of vacuum and the needle does wobble but only about an inch of vacuum or so. The timing doesn't change anything. I did find out about the fuel bowl vent I was talking about earlier. It was used on pre 1970 factory equipped Holley's to try to let the bowl vent when it was heat soaking after you shut it off to try to prevent boiling or vapor lock. This thing has a plate below the carb to convert it to a PCV valve and I'm starting to lean towards the base gaskets. I sprayed some carb cleaner around it but it didn't change the idle. I'm going to pull the carb tomorrow and see what's going on there.
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By miker - 11 Years Ago
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There's been some post recently about wrong size PCV valves. Might be worth plugging that, and see what the vacuum/idle does. It doesn't take much of a cam to require 800 rpm, even my old Y-270 liked it at 900. I'm running a stick, so no big deal.
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By Lex - 11 Years Ago
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I think this engines been apart so it wouldn't surprise me if it had a small cam in it. I ran the valves and the head valleys are clean as new and the plugs all looked excellent and in the 2 years I've owned it I've never had to even top off the oil. I can't stand it though when I think something isn't running just right. It's also been converted from points so I bought a new cap and rotor I'm going to try tomorrow.
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By charliemccraney - 11 Years Ago
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When you have the carburetor off, close the throttle completely and make sure the plates are centered within the bores. You can shine a light from one side and look through the other and that will help you to see if the plates are installed correctly.
Another thing to check, make sure that the secondaries are closed. There is a screw that you can adjust from the bottom to open or close them.
If these check out, then you have a vacuum leak. It doesn't matter what a vacuum gauge tells you, it's pulling air somewhere other than the throttle bores.
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By Lex - 11 Years Ago
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I just found it !! The vacuum line that runs from the back of the intake to the fuel pump had popped out of the fuel pump. Funny how something so simple cost me 3 days of work and worry !! Thanks for all you guys input !
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By charliemccraney - 11 Years Ago
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Does it idle smoothly at a lower rpm now?
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By Lex - 11 Years Ago
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Yep, smoothed right out.
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