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Holley 8007 slow secondary throttle plate closing
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Author:  spacecommander [ Thu Dec 11, 2014 10:38 pm ]
Post subject:  Holley 8007 slow secondary throttle plate closing
OK, temp engine fix until the 2 x 2bbl setup gets the linkage built and adjusted is a different off manifold and 4bbl 8007. Last time I worked on a 8007/6299 was back in the 1980's. The secondary throttle plates seem awfully slow to close. I hear hissss as the plates close. Shouldn't they snap shut?
Author:  slantzilla [ Fri Dec 12, 2014 8:31 am ]
Post subject: 
If the motor is not running, no. The hisss you hear is the vacuum pod leaking down.

IIRC, when running there is a link to the primary side that mechanically closes it.
Author:  nm9stheham [ Fri Dec 12, 2014 11:46 am ]
Post subject: 
How are you seeing this symptom? Not running or ??
Author:  wjajr [ Fri Dec 12, 2014 1:45 pm ]
Post subject: 
Secondaries are closed as fast as the primary throttle plates close via connecting rod that rides in that long half moon slotted bell crank attached to primary throttle shaft. Just a slight primary throttle back-off will close the secondaries when manifold vacuum increases.

Getting back on it and the primary throttle plates are opened beyond 75% of fully open the secondaries will once again slowly re-open over a few seconds.
Author:  spacecommander [ Fri Dec 12, 2014 1:57 pm ]
Post subject: 
Carb is off the car. I see the linkage and half moon slot, but even with the throttle plates (primaries) snapped shut, the secondaries still have about 12-15 degrees of motion left. Think I got it though - the throttle shaft is not centered on the secondary plates - looks like air pressure will "snap" them shut the remaining 12-15 degrees.
Author:  spacecommander [ Sat Dec 13, 2014 8:06 pm ]
Post subject: 
Interesting - haven't seen one of these before - a secondary vacuum diaphragm adjustable bleed screw. It was almost totally shut causing the super-slow secondary closure.
Image
- saw this when installing the fast change kit for the secondary springs.

Image

And here's the truck back from the painters and with the restored ornamentation:
Image
The goal is the 2 2bbl carter/webers on the dual offy manifold, but getting the linkage to work properly and reliably (need real bearings, not shaft on aluminum) is a massive job so the 4bbl offy manifold with either this Holley 8007 or a small 400 CFM Carter AFB will be used. Have run holleys on slants and other cars before, never tinkered with AFBs. Have both. Have re-jetted the 8007 for altitude (5500') but haven't ever played with AFBs before - are they easy to re-jet for altitude?
Author:  wjajr [ Sun Dec 14, 2014 6:58 am ]
Post subject: 
That rod connecting to half-moon slot can be bent in such a way as to fully close secondary throttle plate when primary throttle plates are closed. Idle air and fuel mixture cannot be correctly adjusted if secondary throttle plates are few to flutter.

There is a secondary stop set screw located on choke side of carburetor on bottom flange that limits final closing position of its plates to keep secondary idle circuit and its air fuel mixture stable. With carburetor inverted locate both small idle fuel drill holes and transition slots just below throttle plates. Start with throttle secondary plates closed on stop, and adjust until transition slot looks like a square hole. Remount carburetor and re adjust idle screws and primary throttle stop. You will have to go through this adjustment sequence several times before getting it right. These must not be covered when throttle is full closed, and throttle plates must not be able to full contact wall of secondary barrel bores as at to allow for idle air to enter.


Tips: Here; and here
Author:  spacecommander [ Mon Dec 15, 2014 1:40 pm ]
Post subject: 
Quote:
That rod connecting to half-moon slot can be bent in such a way as to fully close secondary throttle plate when primary throttle plates are closed. Idle air and fuel mixture cannot be correctly adjusted if secondary throttle plates are few to flutter.

There is a secondary stop set screw located on choke side of carburetor on bottom flange that limits final closing position of its plates to keep secondary idle circuit and its air fuel mixture stable. With carburetor inverted locate both small idle fuel drill holes and transition slots just below throttle plates. Start with throttle secondary plates closed on stop, and adjust until transition slot looks like a square hole. Remount carburetor and re adjust idle screws and primary throttle stop. You will have to go through this adjustment sequence several times before getting it right. These must not be covered when throttle is full closed, and throttle plates must not be able to full contact wall of secondary barrel bores as at to allow for idle air to enter.


Tips: Here; and here
Thanks! Will read up on the tips and such and will follow your advice on the secondary setup. Knew the plates couldn't fully close but didn't know how to properly set the gap. I've gone in and replaced the main jets with smaller ones (49?) and a different power valve as I'm at 5500'. Have a 400cfm Carter AFM also, but have never used or tuned a Carter 4bbl before. Familiar with (or used to be ;-) ) Holley, Dellorto and Quadrajets but zero on a Carter. No idea how hard/easy they will be to tune but figure on putting in the heaviest secondary spring in the 8007 to basically shut off the secondaries and see how it runs as a 2bbl at first, then will play with different springs.
Author:  wjajr [ Tue Dec 16, 2014 7:21 am ]
Post subject: 
Yup at 5000 feet one needs to go to a smaller jet. Holley TV has the recipe for how many sizes to step down per 1000 feet of altitude, I just don't recall it at the moment... Old beer infused head in use here, not much help, sorry. But, 49 jet seems close.
Author:  spacecommander [ Tue Dec 16, 2014 9:35 am ]
Post subject: 
Quote:
Yup at 5000 feet one needs to go to a smaller jet. Holley TV has the recipe for how many sizes to step down per 1000 feet of altitude, I just don't recall it at the moment... Old beer infused head in use here, not much help, sorry. But, 49 jet seems close.
Thanks!
Author:  nm9stheham [ Tue Dec 16, 2014 11:56 am ]
Post subject: 
Quote:
Start with throttle secondary plates closed on stop, and adjust until transition slot looks like a square hole. Remount carburetor and re adjust idle screws and primary throttle stop. You will have to go through this adjustment sequence several times before getting it right. These must not be covered when throttle is full closed, and throttle plates must not be able to full contact wall of secondary barrel bores as at to allow for idle air to enter.
This is a good place to start but just be ready to vary from the 'squaring the transition slot shape' as needed to make this work right. Sometimes square is not the exact right setting for a paritcular engine combo.

Interesting on the adjustable airbleed on the seocndary pod.....!
Author:  spacecommander [ Tue Dec 16, 2014 12:47 pm ]
Post subject: 
Quote:
Interesting on the adjustable airbleed on the seocndary pod.....!
Had me stumped. The secondaries just s l o w l y closed. The screw was almost completely closed. I just hadn't seen one before.
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