Before I took my first one apart over 20 years ago I was apprehensive. They are dirt easy. They look more complicated than they are. The power valve takes a little understanding but at high vacuum (idle cruise) the diaphragm closes what is in fact an extra jet. Under acceleration the vacuum drops and the diaphragm relaxes opening allowing more fuel for acceleration. When it becomes cracked or perforated in any way it stays open allowing raw fuel to run in at idle and cruise!
I test them a crude way I suck on then then stick my tongue to it like you do in the opening of a coke bottle (on the diaphragm side) if it clings its still good if it drops off it is bad. Of course you can usually tell just by the symptoms. if the float levels are not to high then it is the power valve.
Float levels are checked through those little brass screws on the side of the float bowls. Fuel should be about even with the bottom of the sight hole.
If your vacuum secondaries are malfunctioning there are kits for it to. There is a little tube in on the passenger side right barrel just above the ventures and as air passes with the main throttle bores open wide it creates a vacuum above the ventures that vacuum works thorgh that tube on the diaphragm in the vacuum canister on the side of the carb, vacuum overcomes the spring in the vacuum secondaries allowing the back barrels to open when needed. Three things cause this to mnalfuntion. the diaphragm cracks or tears, the diaphragm is installed improperly thus not sealing and the gasket at the body of the carb where canister mates to is defective (or lost) Dodgem
formatting link
These places will ship world wide from the US. They both have excellent on line catalogs.
To find carbs and kits online store/ air and fuel delivery/holley For books at summit online store/ books/ holley
This would be an excellent book from Sunmmit! HLY-36-155
$28.69 Estimated Ship Date: Today Overview Brand: Holley Product Line: Holley How-To and Reference Manuals Title: Super Tuning Holley Carburetors Author: Alex Walordy Pages: 68 Binding: Paperback Quantity: Sold individually.
Learn more about Holley fuel system products.
Book, "Super Tuning Holley Carburetors", 68 Pages, Paperback, Each
Have you ever wanted to know how to rebuild a carburetor? Set up a car for bracket racing? How about exploded illustrations of current Holley carbs? These Holley how-to and reference manuals have you covered with in-depth technical information and plenty of photos and illustrations.