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Username Post: Sqealing Holley 4555        (Topic#369516)
ranman 
"2nd Year" Silver Supporting Member
Posts: 10888
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
09-16-22 10:09 PM - Post#2847424    

A friend has one of those infamous/controversial 1970 or "1970 1/2" Z28s
Two years ago, I spent the better of two weeks helping him get the car started for the first time in 5 years. There were big time issues because I knew nothing about the car prior to me helping him with it.
The 1970 Z28 have the LT1 option with 11 and 1/4 to 1 compression and a quite large Holly 4555, 780 CFM carburetor.
Prior to me helping him I found out some major issues through the traditional search and destroy methods. At some point a few years earlier, he had cleaned the carburetor out with soap and water. No, he doesn't own a compressor. ????
Anyhow with that background I discovered major issues, such as the accelerator pump needle was rusted into place and after numerous and I mean numerous attempts at adjusting the carburetor I found the major issue was the two Bass to body screws were in the wrong positions. Two are blind holes, and two of them go into the fuel area inside the carb. He had the screws in the wrong holes. With a huge undiscovered fuel leak, that week of diagnostics allowed a gallon of gas past the rings into the oil pan.
Ok, we got the car running and it ran well.

Ok, let's skip forward to now. The car hasn't been started for two years since we messed with it. It started and ran fine. That's good.
There is an annual event and a cruise in town tomorrow. I wanted to check the idle mixture screws. He said he had tweaked them.
Well, the highest vacuum reading is with the adjustment screws 1/4 turn open. That's with the throttle plates closed.
After a couple house of messing with it, time to call it a day.
Gave the engine a short rev and on deceleration, this nasty ear piercing squeal comes on. It takes from 2 to 30 seconds to go away.
It didn't do this piercing squeal before we began tweaking the screws. I know it's a coincidence but it's driving us nuts. This high pitched, piercing squeal begins as the engine revs down after a quick throttle blip. Vacuum would of course be high at this point.
I squirted water around the carb base figuring a gasket leak.
Yes the carb needs another rebuild, but in the mean time why this squeal? Sounds like it's coming straight out of the carb throat.




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If plants ruled the world, would they regulate oxygen?


 


ranman 
"2nd Year" Silver Supporting Member
Posts: 10888
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
09-17-22 07:57 PM - Post#2847447    
    In response to ranman

.....short version. When you rev the engine, the carb emitts a high pitched whistle or sqeeling sound as it slows back down. Sometimes the whistle continues at idle and eventually stops.
Any ideas?

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 
bobb 
Super Senior Member
Posts: 6126

Loc: paradise
Reg: 09-05-03
09-18-22 11:32 AM - Post#2847474    
    In response to ranman

i would guess more than likely its the butterfly adjustment. maybe an idle air jet. plug the air jets one at a time and give it a blip.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


Edited by bobb on 09-18-22 11:33 AM. Reason for edit: No reason given.

 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10888
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
09-19-22 08:41 AM - Post#2847521    
    In response to bobb

The primary butterflies are almost totally closed to get the idle where it should be.
It's time for a rebuild, even though we did that 2 years ago. Well, actually it wasn't a rebuild it was a hunt and search. I was totally unfamiliar with anything that had previously been done with this carburetor. He had been taken apart, cleaned, and put back together then it sat for years.

As I'm recalling all of the fixes we did, like wrong gaskets and seized up accelerator pump needle, I just remembeed something. He put the two center screws in the wrong holes creating a humongous vacuum and fuel leak. When I discovered the position of the screws was wrong, I pulled them out and put them in the correct holes. The change was dramatic.
Problem solved, sort of.
I'm wondering that if the screws were in the wrong holes for a couple of years and I simply relocated them, the gasket had already been crushed by the pressure of the screws being in the wrong location for so long. By that time the gasket already had a crushed permanently and we didn't replace that gasket. I simply moved the screws to a different position. Maybe that plate to body gasket is vibrating like the reed of a clarinet. Actually it sounds more like the whistle of a teapot. ????
The engine idles best with the idle air screws are less than half a turn open so, something is leaking inside. The exhaust burns your eyes like pepper spray.
I've been doing a lot of googling and carburetor warpage with these Holleys is mentioned a lot. I think that needs to be checked out when we have it apart.





~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 
Don57 
"17th Year" Silver Supporting Member
Posts: 1425
Don57
Age: 72
Loc: Illinois
Reg: 04-28-00
09-19-22 04:13 PM - Post#2847546    
    In response to ranman

Is it possible that the screws that were incorrectly put in the blind holes were too long and they may have cracked the body?

Don
1957 3200 Stepside


 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5547
Mel Foye
Reg: 09-29-00
09-20-22 06:45 PM - Post#2847600    
    In response to ranman

From my real 69 Z 28, A/F screws 1 and 1/2 turns out, primary and secondary were a small amount open.
At this point I would suggest he turn that carb to a professional. In the past several good ideas were given but that is not the same as having the carb in your hands.
Also did he ever set the timing up? Good luck. Mel




It Was On Fire When I Laid Down.


 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10888
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
09-21-22 08:03 AM - Post#2847621    
    In response to Don57

There the original screws and I'd bet Holley uses the same screws for all four center positions.
Whenever we get around to it, I'm gonna be in Columbo mode. Thanks.

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


 
ranman 
"2nd Year" Silver Supporting Member
Posts: 10888
ranman
Loc: The cold wet and windy O...
Reg: 03-10-01
09-21-22 08:14 AM - Post#2847622    
    In response to Mel Foye

I'm that pro, Mel.
If the carb hadn't been tinkered with, and I was the person that took it apart, I probably wouldn't be here asking questions. ????
I recall setting the initial timing at 12. He has an MSD ignition system and distributor. I don't recall how much I put into the vacuum can. Possibly 10 degrees. I'm guessing 34/36 total.
Vacuum advance is manifold. The factory carb doesn't have a ported connection.

~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~
If plants ruled the world, would they regulate oxygen?


Edited by ranman on 09-21-22 08:26 AM. Reason for edit: No reason given.

 
Mel Foye 
*VIP* Original Founding Member Group
Posts: 5547
Mel Foye
Reg: 09-29-00
09-23-22 02:22 PM - Post#2847710    
    In response to ranman

With focus only on the --squeal-- and that it takes some time to quit I lean toward the vacuum diaphragm for the secondary.



It Was On Fire When I Laid Down.


 
IgnitionMan 
Valued Contributor
Posts: 4007

Reg: 04-15-05
09-23-22 02:55 PM - Post#2847711    
    In response to ranman

What is the setting on the secondary throttle plates???

This is for a Holley vacuum secondary carb, also applies to an early double pumper with only primary idle screws.

Unlike the primaries, the secs do not contribute to idle settings. The stop screw is only there to stop throttle plate binding in the base plate bores, NOT to supplement idle air.

To correctly set the secs stop, back it off, and completely seat the secs throttle plates, bind them up in their bores.

Then, bring the set screw to ZERO additional opening, and then, add 1/8th positive turn to open the plates. NO MORE.

This sets the secs properly, so they do not bind in their base plate bores.

It sounds like air flow past a pair of butterfly's is getting to full sonic speeds, and making noise.





 
bobb 
Super Senior Member
Posts: 6126

Loc: paradise
Reg: 09-05-03
09-24-22 10:18 AM - Post#2847731    
    In response to ranman

primarys need to be open enough to expose the transfer slot. the slot opening should be about square.

70 L camino, grampa engine, g-force 5 spd, road rage suspension. Pray first before all else fails.


 
IgnitionMan 
Valued Contributor
Posts: 4007

Reg: 04-15-05
09-24-22 05:25 PM - Post#2847747    
    In response to IgnitionMan

I have a dandy picture of the primary butterfly's in a Holley, showing the proper setting for ITS, but, have absolutely NO idea how to post it.

It is on my computer, NOT a "URL"?????????



 


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