Holley Secondary's won't open

[tarafied1]

Did you do your test with the primaries wide open? Many Holley's have a pin or linkage that will prevent the secondaries from opening unless the primaries are open. Some have choke "lock out" linkages as well.

Yes, did you see the video of the bench test? The 770 and 750 both have a linkage that force the secondary to close. Also the choke could restrict the airflow and cause the flow thru the primary to be low enough to not have enough vacuum signal. I manually adjusted the choke wide open on street tests. On the bench test the air hose doesn't care where the choke is. There is nothing on these carbs like a lock out or pin or anything else to restrict the secondary's (other than the afore mentioned link). I did confirm that the throttle linkage is working and the primary's open all the way on the car. No binding or restrictions on the manifold, etc. The secondary's are free to move. All they need is a low pressure signal above the diaphragm to over power the spring. Also as mentioned they do open or attempt to open with no spring confirming again that everything is free to move as designed.
The only logical thing left is the possibility that the port is restricted enough to prevent the low pressure needed. It's not blocked completely as air from the compressor and fluid from the carb cleaner will come out of the ports on both the primary and secondary side. That or there is a vacuum leak in the system. The seal is good. As I mentioned I can switch the vacuum diaphragm body to the 750 and it works. the cork gasket is staying with the diaphragm body. I can put a vacuum pump on the diaphragm body and create the movement. So it's not in the body or the check ball or the spring or the linkage, etc.
It has to be a problem in the carb body itself. The lead plug vsiually looks intact. The air and fluid do not leak past it. I can't see any other points where fluid or air could be getting past the machined ports. That leaves me again to think the primary port is restricted somehow.

 

[bartl]

Brainstorming a bit... your test with carb clean seems to verify that nothing is plugging the vacuum passage so it would seem to be either a leak or restriction in the secondary vacuum "motor" itself or not enough of a vacuum signal is being generated in the throttle bores.

 

[tarafied1]

yeah, I can't figure this one out. The ports appear to be clear. I did clean it real good and put it back together. I tested it again and it still won't open the secondaries. I can take the whole assembly off and put it on the 750 and it works. I can use my vacuum gauge and create a vacuum and it works. I can get both the 750 and the 770 "vacuum motor" to work on the 750 but neither will work on the 770. The thing tries if I have no spring at all. I can also "help" it by pushing it open when I am blowing air but it wont stay. There has be be porosity or a crack or something in the 770 body causing the vacuum signal to be too weak by the time it gets to the diaphragm.

 

[rbohm]

this is why i gave all my holleys the old float test and switched to edelbrocks. the edelbrocks use an air valve secondary that opens and closes due to air flow through the secondary side and doesnt depend on vacuum running through the primaries.

 

[tarafied1]

I'm not quite ready to to go to that extreme and switch to an Edelbrock carb. I did buy a Demon for my 72 Chevy though. It works a lot like an Edelbrock. Well I didn't actually buy it, I won a coupon for it at a car show. I had a Holley 600 on there before. I can't say that I notice any difference in the way it runs but it is a tired old 350 with no horsepower. I think I will stick to Holley on the 429 unless I go EFI.