Hmm. Not so sure about that one. The whistle was coming from the carb throat. I and several others checked for vacuum leaks. I had the 750 rebuilt and the whistle went away, as did the performance problems.

 

likely cause was the base plate may not have matched the carb , causing a manifold leak. it happened to me. the baseplate left a 1/16 " gap along the front edge of the carburetor. caused a definite whistle. no amount of spraying wd40, or carb cleaner,failed to detect the leak, because it was too large of leak. I had it at a reputable shop, and they failed to find the leak. I knew the symptoms were a vacuum leak, so when I got it home, I pulled the carb and discovered the problem. replaced the riser with one that fit, and now it runs great. the point is , a smaller carb will work fine. the only time the bigger carb is needed is at high rpm, and these engines don't turn up high enough to need the extra cfm. If the 750 cfm carb is working for you , that is great, but a 600 cfm carb will work too, as that is what I am running. I plan on mounting a 1 gallon tank under the hood to see how far I can get on a gallon of fuel . I will be running with the truck empty,but it will give me an idea of what my gas mileage is going to be.

 

That is very common on Hollys as the whistle comes from just when you open the throttle a little the butterfly goes past the idle ports and causes a whislte. The stock carb I have been told is ether a 600 or 625 CFM. After 3 rebuilds on this one in mine it seems to be working ok for a Holly but id it dies again its getting a AFB. Done enough Holly rebuilds over the years to get to know them too much..

 

It is possible that depending on the carb, the idle circuits were too small to feed all those 534 inches. In that case, you'd have to crank the throttle open and "idle" partly on the main circuit, that could have been the whistle with that small 570sa on there.

The 750 double pumper is set up to feed a big block with a hot cam at idle so it has pretty fat idle circuits, maybe just about right for a 534.

I show the 570 Street Avenger as the same venturi & throttle sizes as Holley's normal 450cfm (at 1.5" Hg) carb.

I also have down that this is the size carb (450cfm Holley) that came on the 534, List 1860. From this thread

https://www.ford-trucks.com/forums/6...4-jetting.html

It says the 534 Holley came with #45 and #61 jets, though that seems lean in the primary even for a 450 Holley. Maybe #55?

Maybe the 534 came with a bigger 600cfm Holley later on - the 460 Ford Truck used a 600cfm Holley 4180c carb as late as the mid-1980s. Anybody know for sure?

In any case, I would not worry about the size, especially if holding the rpm below 3600. My computer, the WerbyFord Gonkulator, shows the 534 GROSS horsepower peak as:

341hp at 3900 with 450 Holley (stock cfm??)
355hp at 4000 with 600 Holley
361hp at 4100 with 750 Holley

Those are not big differences and will be even smaller at 3600rpm - having a good running and idling carb is more important than that for the use of these.

 

I installed a 600 cfm holley to replace the worn out 650 cfm holley previous owner installed. those horsepower numbers would come at a high cost if you were able to rev it that high! I never rev my 477 over 3000 rpm.