While am finishing the 3x2 94's on the 57 Bird I am using a Holley 4bbl list #1848. This is the replacement carb sold by the Tbird restoration parts companies. The carb is about 6 years old. I have the vacuum advance line from the distributor connected to the port on the upper passenger side on the front metering block. This port has vacuum at any idle speed. Is this right? I am fighting a bad hesitation.

57 Black Tbird 312/auto

Mark

Nice car and thanks for the pictures. You asked about where to source the vacuum for the distributor. I have mine hooked to full time manifold vacuum and it works for me. I was told that the car companies went to ported vac to meet EPA requirements in the 70`s. So unless you are in that situation,then why? I found this info online and you might be interested.

http://www.corvetteactioncenter.com/forums/c3-technical-performance/60830-ported-vs-manifold-source-vacuum-advance.html

Pete     55 Tbird with aircooled FOM, 57 312, mild cam, 57 tach drive distributor with Pertronix (basic module) and Holley 600 vac secondary, Dana 44 with 3.31

Mark MB - If the ported vacuum source on the carb (the one you described on the primary metering block) is providing vacuum all of the time - then the primary throttle blade is too far open. That causes the "port" for ported vacuum to be perpetually open - and trouble with idle transfer - the hesitation you mention.

The primary blade needs to be accurately positioned on the idle transfer slot to make both functions work properly. If you can't keep the engine running with the blade positioned as shown below, you will need to open up the secondary blades slightly to provide more air. There is some fuel available there - and you will make up the rest with the mixture screws on the primary.

There was a time when - if you couldn't get enough air with the primary blade in the right spot - guys would resort to drilling holes in it for additional air passage. Don't. There is a provision in most vacuum secondary Holleys to "stop" the rear throttle shaft with a hidden adjustment screw. It is on the passenger side immediate;ly behind the throttle rod exit from the base plate.

 

I have learned that making the screw adjustable with the carb mounted - isn't the easiest thing - but it is worth working out. My hillbilly solution is to replace it with a piece of machine screw ("all thread") that protrudes out the bottom, and you can then turn it with needle nose pliers. Other ways work - and may be more sanitary - but my way does work (at midnight when the hardware store is closed).

When the primary blade is properly located, and you have the idle speed controlled - set the two mixture screws for best vacuum. and go from there. Make sure your timing is set before you quit adjusting the mixture.

 
 Steve Metzger       Tucson, Arizona

Steve,



Thanks. I followed your detailed description for this procedure with Pops(Clay). I will take the carb off and have look.



Pete,



Not sure of which vacuum source I will use but want to make sure the carb is working right first. The article on ported vs intake manifold vacuum is very good. I will probably try it both ways and see what happens. Thanks.

57 Black Tbird 312/auto

Mark - Depending on the vacuum provision (ported or unported) - you may wish to set the distributor up for different amounts of mechanical advance. For instance:  

Assuming the maximum desired total advance is 36° - and you use ported vacuum - then you might get a good running set-up at 14° initial and then 11° distributor /22° crank for the centrifugal advance. Resulting in 36°.

If using live manifold vacuum, then setting the initial at 10° and the centrifugal for 13° distributor /26° crank will net the same total of 36°. However - the vacuum canister will be active and kick in some advance at idle - which results in more advance and perhaps a bit more vacuum. 

In both cases, watch out for a vacuum can that adds too much advance. When you have increased the initial way beyond the factory 5° or so, that increase will push the maximum possible advance way up there.  

Your tri-power set-up - the center carb may not have a choice of ported or unported - and if that's the case, I think I'd use the live manifold vacuum to avoid a lot of re-tuning later on.   

 
 Steve Metzger       Tucson, Arizona

Steve,



This is good stuff. On the tri-power, I am modifying the center Holley 2110 using Ted Eaton's instructions he posted here for ported vacuum.



http://www.y-blocksforever.com/forums/Topic39105-3-1.aspx?Highlight=94+vacuum

57 Black Tbird 312/auto

I've only had experience with 57 Tbirds, but every one I've seen has the distributor vacuum advance line in the spot you indicated.





54 Victoria 312;  48 Ford Conv 302, 56 Bird 312
Forever Ford
Midland Park, NJ