Try 10 degrees, but listen carefully for "pinging" Should help. Do you have the exhaust crossover blocked? If so that will cause you to need a slightly richer misture. AND, make sure you have the vacuum blocked off when you set the initial timing.  

Read your last post.  The car was OK until the carb was rebuilt, has not been OK since.  If nothing else was done, then don't try to cover up the problem with other changes.  Sort out the carb issue.  Also, I don't think the 390 was a "double pumper".  A double pumper has an accelerator pump on both the primary and secondary fuel bowls, and is usually a mechanical secondary instead of a vacuum secondary carb.

John in Selma, IN

The ECZ-V carb is for '57 passenger and T-Bird, 312, Fordomatic.  Sounds like the original carb for your car.  It is valuable, I would keep it just because it's the original.  If you ever go for concours judging, or some subsequent owner does, that carb is a must.  Replacements have a different fuel inlet direction, a dead giveaway to a judge.

There are air bleed holes in various places in the carb, and if they are partially restricted because of insufficient cleaning, they can cause rich mixtures.  Inneffective idle screws usually point to a leaky power valve or gasket, but there can be other causes too.  Is the car hard to start after sitting for 10 minutes, and blows black smoke out the pipes when it does start?

John

     I rebuilt one of these for a fella about twenty years ago. Not being familiar with the original Thunderbird Carb, which that is, I reversed the jetting. All modern Holleys have larger secondaries, and smaller primaries. You carb does not, the primaries are larger than the secondaries and require the larger jets be in the primaries. That may or may not be part of the problem. Second, if the floats in the primaries were set incorrectly, then the secondaries are probably also wrong. Third, replace the power valve with a NEW 6.5 as per original and be sure to replace the gasket. Last, make certain your "expert" put the correct gaskets on the metering plates and float bowls, it's simple to mix them up. I'd also get a cat of carb cleaner and check to be sure the idle circuits and air bleeds are open and not blocked. Somewhere in there I think you'll discover the problem.

    I think that the carb is somewhere in the 400 cfm range, most guys who replace them go for something in the 500 cfm range in a newer Holley, Demon or Edelbrock (the old Carter AFB. Pony carbs in  NM can rebuild these. They aren't cheap though. You can google or do a search for both Holley and Pony Carbs on the web.

The power valve gasket being the incorrect one or possibly not seated properly would be an easy item to check.  If when pulling the metering block loose from the main body and finding it wet in the power valve cavity, then look hard at the power valve itself for either a ruptured diaphragm or a faulty pv gasket.

Another item to check for is a power valve that is bottoming out in the power valve chamber which in turn is not allowing the metering block gasket to fully seat when being tightened down with the bowl screws.  This can be as a result of a replacement valve that is thicker than the original or gaskets that are too thick or multiple gaskets being stacked on top of each other.  Just putting the metering block up to the main body with the power valve installed and seeing that the metering block is flat against the body without a metering block gasket in place should suffice for this check.

    You are getting a lot of advice and solutions to fix a problem you may or may not have. Can you describe in painstaking detail just what the problem is and when it happens. I get the impression that on COLD startup you get a very rich mixture, and black soot and a strong gas smell. Could be a choke issue. After it warms up then it gets somewhat better but is still over rich. Is this right or not. Still could be the choke. You say the car was restored a while back and that you have had the carb rebuilt. Was the car better before the carb rebuild? And why did you have it rebuilt?  In the time that you have owned the car, did it drive OK and gradually get worse or just got bad in a short time? Remember you chance of getting the RIGHT ANSWER to "YOUR PROBLEM" is how well you describe that problem. Try again please. Pete

  I was just looking in the 1957 Ford shop manuel for info on your Holley. Your carb has TWO power valves a primary 8.5 inch of vacuum to open and a secondary that opens at 10.5 inch. The idle mixture needles are turned IN to lean the fuel mixture and OUT to increase mixture richness. Preliminary setting is full in to JUST touch then out ONE turn. Your rich condition is a float level, BLOWN power valve(one of TWO) or dirt in an air bleed passage. KEEP your present carb and GET A NEW MECHANIC. This is a very simple carb and if the guy can`t fix it by now find another guy to work on it. Pete

Carb kits are resonably easy to install if just taking care to remember where the small parts go.  The manual Mark mentions will definitely be of assistance for first timers.  Just be sure to clean all the carb components thoroughly before reassembly though.  The spray carb cleaner with the tube installed on the nozzle works well for this.  And insure that the primary and secondary metering blocks go back in their respective positions on the carb.  Check the flat surfaces with a straight edge to insure that warpage is not present.  Minimizing the amount of time between tear down and reassembly also helps.  Don’t tear the carb down one day and put it together the next especially if you’re unfamiliar with a particular carb.