I have a large pile of 4 bbl carbs (mostly new) at my disposal. I have at least one of every major brand. I was comparing them side by side, and got to wondering which style of primaries/secondaries would give the best gas mileage?
When I turn them upside down, and compare the butterflies, I see on one carb. where the secondaries are the same size as the primaries. Then I see where the primaries are tiny, and the secodaries are huge.
And then I see the secondaries are just a tad bit larger than the primaries on others.
What style is best for a Jeep V8 304, that sees a bit of everything? When I say best, I mean a mix of good fuel economy, and off road performance.
Would the answer be the same if the engine was a 360?
When the bores are the same size, we call that a 'Square Bore'
When the primaries are smaller than the secondaries, we call that a 'Spread Bore'...
Smaller primaries will give better fuel control and mileage if you don't put your foot in it and open the secondaries.
You should also be working the throttle linkages,
Watching the throttle valves (Butterflies),
Some will only open the primaries, these are VACUUM secondaries.
If the linkage opens BOTH sets, then it's MECHANICAL secondaries.
Some pictures would help us to identify the carbs...
You will probably be looking at a few basic types of carbs,
Holley, Rochester, Carter, Motorcraft, ect.
had two basic types of carbs, the AFB and the Thermoquad,
ThermoQuad is easy to identify, it has a 'Plastic' venturi body (actually bakealite) to keep heat away from the float bowls.
The AFB is being reproduced by Webber as the 'Edelbrock Performer' carb...
Still leaks like a sieve and is hard to tune... But it's out of under patent, so it 'Open Source' now and anyone can reproduce it.
is pretty easy to identify, they usually cast 'Holley' right in the float bowl,
Once you know what you are looking for, it's VERY easy to spot the vacuum canister on the right rear of the carb to know if it's mechanical or vacuum secondary.
Every Holley comes with a list number facing forward on the choke horn that will tell you EXACTLY what you have in your hands.
carbs were often Holley designs, but made more simple for lower cost of production,
About every Motorcraft carb made worked pretty well, with the exception of the 'Vairable Venturi' model... Easy to identify, one large opening with long rectangle throttle valve in the venturi bore.
is GM's primary builder, and that includes the famous (or Infamous, depending on how you look at things...) QuadraJet and DualJet carbs.
QuadraJet carbs came in three sizes, Large, Huge & EXCESSIVE!.
You can still find sites that will run the numbers down for you.
Like I said, pictures might help us help you with your parts sorting chores.