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Holley secondary's won't open

7K views 29 replies 8 participants last post by  TARA-fied 
#1 ·
I have a 18 year old Holley 770 Street Avenger vacuum secondary. I have verified the secondary's won't open. I used the paper clip on the linkage and it didn't move. I bought a new diaphragm but when I pulled the housing off before splitting it open, I checked it with my vacuum pump/gauge and it works. So I replaced the little gasket between the housing. Blew some carb cleaner back thru the hole and verified the passages are open. I put it all back together and it still didn't work. I took it back off and tried blowing air thru the venturi above the small port. Stiil didn't work. I replaced the diaphragm anyway, still didn't work. I took the spring out and put a yellow spring in (lightest). Still didn't work. Took the spring out completely and it moved but didn't open. I have an old 750 on the shelf so I checked it. It worked. I swapped the housings between them and the 750 will work with both but the 770 will not work with either.
Any ideas what's wrong with the 770?
 
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#2 ·
Did you confirm that you can manually open the secondaries while the carb is bolted to manifold (no interference)?
Make sure the secondaries don't close so far as to jam themselves in the bore.
 
#3 ·
Thanks, yes, secondary's open on the intake manually. I checked and rechecked that as well as if the primary's open all the way with the throttle linkage. Also I have actually opened the secondary's a bit for idle speed (big cam overlap). Nothing binds or is jammed.
One reason I went to checking with the air nozzle was to eliminate a lot of variables. It seams to be a problem with the carb body I am thinking. They will try to open (using the air nozzle) with no spring at all. You can see them sort of flutter with the yellow spring but not open. It seams there is not enough low pressure drop (vacuum) coming from the venturi. The carb has been on the car a long time but has never been rebuilt. I did blow air and carb cleaner thru the hole while the vacuum diaphragm body was off. It looked clear, at least air and carb cleaner come out of the holes in the venturi, but the secondary's are defiantly not working right. I did the air nozzle test on the work bench. Side by side with the 750. The 750 works like a charm, the 770 does not.
As stated I swapped the diaphragm body between the two and both work on the 750, neither work on the 770. I thought maybe the parts weren't making a good seal or housing was bad or any number of things but I can swap parts directly to the 750 and it works. Parts that work on the 750 I can put on the 770 and it doesn't work.
Thanks
 
#4 ·
I don't have any more advise - other than if the carb is 18 years old, you got your money out of it. Maybe someone else will have some advice for you.

Other wise, I suggest you use the 750 body and build up a working carb from that.
 
#6 ·
yes, you are correct. There is a part of the linkage connecting the primary's to the secondary's. Mostly I think to close them because once they are open the port in the secondary venturi will keep it open. But yeah, that isn't it. I did my bench test on both carbs with the primary wide open. Also verified when on the car at WOT the secondary's will open manually. Thanks though
 
#11 ·
yes. the the vacuum diaphragms both work. They will work on the 750. I did check that before changing the diaphragm. In the video I posted you can watch it open.
 
#12 · (Edited)
interesting I never heard of this. However, my 770 used to work so I don't think that not having that brass nipple/tube is the reason it doesn't work anymore. The 750 doesn't have one and it does work. But the whole thread is a great read and does get me thinking the port might be restricted on the primary side. Thanks for sharing that! I might drill out the lead plug just to inspect the hole. I have nothing really to lose at this point!
 
#13 ·
Tara-fied if you can get access to a carb dip tank you might try disassembling it and soaking the main body overnight and using the spray cleaner and air in the passage again any obstruction in that passage no matter how slight may cause your problem, eductor type devices don't respond well to any obstruction, also closely examine the venturi area of the bore for any nicks,burrs,or any other kind of damage that may disrupt airflow near the passage,small damage may be able to be smoothed out with emery cloth,larger damage may require more extensive repair that rapidly becomes a matter of diminishing returns.Also check the end of the passage next to where the diaphragm housing bolts on you will see where they drilled the passage and plugged it with a piece of lead or soft metal make sure that plug hasn't gotten loose and is leaking, a backfire can cause a holley to do all kinds of weird things simply because it ruptured a power valve diaphragm or loosened a plug.
 
#14 ·
THANKS John!!! I inspected it tonight. The lead plug "looks" okay. The venturii looks fine and feels okay. I will disassemble and try soaking it. Any recommended product? I don't know any shops that still rebuild carbs but back in the day I used take carbs disassembled to a local parts store and they would soak it.
 
#18 ·
I'm not discounting that it might be an improvement or different at the very least but I don't understand what you mean when you say that it is essential. The 770 worked for a long time without it. Also the 750 works without the brass nipple. I have had other vacuum secondary carbs that work without it. Now maybe the brass nipple will change when or how quickly it opens for optimizing the performance and in that respect it might be essential but for it to simply function it is not essential.
 
#16 ·
I think the issue is the test method. Put it on the car, put your paper clip on and go for a romp. See if it opens then.
 
#19 ·
Pull the carb, remove vacuum actuator, using brake clean verify the pasagway is clear to the venturi. May also need to remove throttle plate. It only takes a couple months for gas to dry and cristalize to block the time ports. A single carb backfire can mess up several small ports.


Sent from my SM-G920V using Tapatalk
 
#20 ·
thanks, I have blown air and carb cleaner thru there. the port is not 100% blocked as I do get air and cleaner coming out. I have the carb apart right now, Going to get a gallon of carb cleaner and soak it.
 
#22 ·
both mine are different also. one has the check ball the other is like the second from the front. But they both work on the 750 and neither work on the 770. Something is just wrong with the 770. I have cleaned thoroughly and it just wont work. It has to have a crack or porosity or something preventing the vacuum drop.
I'm using the 750 but it doesn't run as well with the 750. But at least the secondaries work. I'm thinking I will buy a new 770
 
#23 ·
Tarafied you might want to consider going up to an 850 if you have to buy a new carb anyway,can't imagine there being much difference between the 750 and 770 unless the calibration is really different.If both carbs are calibrated the same and it likes the 770 that much better it may be an indication that the motor would like an even bigger carb?Normally I would agree that a 750-770 carb should sufficient for a mild 429 inch engine but you've made some pretty hefty upgrades to the top of the engine,and it may want more.Just something to consider and research before you go out and spend your hard earned cash.Look at the L-88 427 chevrolet for comparison you probably have as much or more head than them and more cam and GM specced a vacuum secondary 850 for them.
 
#24 ·
Thanks John, I hadn't really given that any thought. I guess an 850 isn't a big jump and you are right, I did a lot to get it to breath better.
 
#25 · (Edited)
Before buying another carb, trying going here first with your Holley ?'s. Many great folks there with a wealth of carb knowledge.
racingfuelsystems.myfunforum.org - Index page

Hope this helps.

You can also go here to find if other had similar issues and the advice they received, but be prepared for some possibly eye-opening and/or surprising info.
Index
 
#26 ·
thanks, looks like a lot of good info. It may take a while to find my specific issue if it's even something someone else experienced but still a lot of great info.
 
#28 ·
yeah I saw that link earlier. I could try that and it may help. I am not accepting that it "will not function correctly" with out it because it worked before and the 750 works fine without it. I also hate to do all that work to the 770 and it still not work because of whatever is actually wrong with it is still wrong.
I mean I suppose I could try it, I am only out the time really, materials are minimal.
Thanks though, I am thinking I will still buy a new carb that works and then when I am bored I might mess with the 770.
 
#30 ·
well the secondaries don't have any port(s) thru the base plate or metering blocks. It's only the one between the body and the vacuum housing. Little round gasket.

I drilled out the lead plug to check for blockage. Didn't see anything. ran a small wire thru it. I am going to tap it and put a set screw in and see if I can get it to work. I might go ahead and do the brass tube mod since I am this far!
 
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