Did you notice that post from "Marc" regarding his rebuild? Started and ran and kept dying.Turns out the Pertronix went bad even though it started and ran."Pops" has a Pertronix in his.Same problem maybe?

  

I'm back in the saddle again.......



I saw this:











And selected this:







Out of the box, the stumbling is gone and the surging at cruise speeds is also gone!



4160/465 cfm with adjustable floats.



The only MINOR issue is I can't get the idle down to the 500-600 range. Idle adjusting needles are set properly, the throttle stop screw is just off and not touching the throttle arm, fast idle screw back way off. There is no secondary adjustment available on throttle body. Lowest I can get it to idle is about 900 rpm.



You guys really taught me a lot in this thread. I think the suggestion to down size the carburetor was excellent. And, all of your collective other suggestions has made me much more confident and knowledgeable. Thank you all!!

pops (AKA) Clay

'56 Thunderbird

Clay - Many of the Holleys of recent manufacture have a secondary throttle stop screw.

It's located back by the vacuum secondary pot's attachment to the secondary throttle shaft - passenger side of the carb.

 
 Steve Metzger       Tucson, Arizona

What is your timing set at?Try backing it down to about 12.That should bring idle speed down a little.Before you touch timing check the throttle linkage.Are you sure the fast idle speed screw is backed down?Almost sounds like the fast idle is still in play.One more suggestion.Disconnect the throttle linkage at the carb  and see if the idle drops.Sometimes the rod will not allow the carb to return to full idle position.If the idle speed screw is not touching the throttle arm it does sound like its not returning all the way to idle position.Check the linkage and make sure its not hanging up somewhere,

  

I backed the fast idle screw out until it un-threaded itself, then screwed it back in only enough to have some spring tension on it. The timing suggestion sounds good since it is presently at 16. I did not see the screw Steve mentioned on the bottom of my carburetor. I had the throttle linkage disconnected when checking the idle rpm. I don't think the linkage is an issue.



I did put about 80 miles on it today without a hitch. Seems to be running, starting and shutting down great!

pops (AKA) Clay

'56 Thunderbird

Clay did you work out what your total mech advance was? If your dissy is standard do as Mark said as Im sure you will have a little too much and you should be closer to your idle speed.



"Came too close to dying to stop living now!"

And the fast idle adjusting screw on the other side is completely off when the choke is in the "off" position?On my 390 Holley you have to open the throttle butterfly completely to access that fast idle screw with a box end 1/4 inch wrench.For it to idle at 900 RPM seems more than just advanced timing to me.If the idle speed screw is not controlling the idle speed which its not if its not in contact with the carb lever something else is holding the RPM higher.If you had turned the carb over before installing and looked just above the throttle plate you would see the "transition" slots in the carb throat.The throttle plate should be adjusted with the speed screw so you only see a "square" box below the throttle plate in the closed position.The idle speed screw should not be turned in(raising idle speed) any further than that point preferably.Thats why its a good idea to note the position of the idle screw when set to the preferred position so you do not turn it "in" any futher than that position.You can turn it "out" reducing idle speed if its too high but usually idle speed is very close to correct with the screw set at that position.Thats why I am thinking something is affecting the idle speed because you say the screw is only in enough to put tension on the spring.Anyway it sounds like you have found your problem which I am sure you are relieved to have solved.Little more fine tuning and you will be set.Now you are a "Y" guy with knowledge.Welcome to the club.The secondary speed screw that Steve is talking about is either recessed in the base or it may not be there-just the threaded hole.Thats how mine is-I just got hold of the proper thread machine screw.I ended up not needing to use it.

  

I recall the slots at the bottom of the throttle bore, but did not know that only a square should be visible.



I think I will confirm the total timing, and bring the initial advance back down to ~12 degrees and see what this does to the idle.



Removing the carburetor is getting pretty painless, so if the idle is not corrected by reducing the initial timing I will take the carburetor back off and confirm the existence of a secondary idle screw and give a good look to see how much of the slot is showing when the throttle plates are closed.



Today, it is off to a car show with no stumbling or surging.

pops (AKA) Clay

'56 Thunderbird

You might try rechecking your vacuum at idle, bet it's a little low.  Nothing screws with your idle like a vacuum leak.  Simple thing will likely get you from where you are to done and happy.  Step by step as has been well discribed by others here.  MIKE, P.S. how are you posting these great pictures??

Mike, still lovin his 57 t'bird after 53 years!

Clay - This is the set-up technique for the idle transfer slot, shown on a diagram. When the primary idle screw is set to provide this function, you'd like to leave it there.....Which then may cause you to need a another way to control air into the carb. The little secondary stop screw shown previously may or may not be fitted to your carb - but inserting one from the bottom with a type of head that can be accessed from outside when the carb is bolted down is a useful tuning tool.

The idle speed being up makes me suspect a vacuum leak as well. You might try using a plumbers propane torch (off) to introduce  some fuel around the manifold seal - just to see if the speed jumps up somewhere.

 
 Steve Metzger       Tucson, Arizona