Which Quadrajet design is best

[rajon]

I haven't tuned a Quadrajet in more than 30 yrs, but I've been collecting them every chance I get whenever there's one to be found for free or less than $5.
So now I've got a few of them and I have a truck that I want to use a Q-jet on.
I live at sea level and that is where this truck will see 95% of it's use.
The truck is smog exempt, being that it's 40+ yrs old.
The engine is a 327 with 8.5:1 compression and some headwork and shorty headers and a Performer intake..
The transmission is a 700R4
I have a couple Q-jets that are from roughly that year/model truck that would work, I'm pretty sure.
But I also have some later design carbs that could be rebuilt and tuned as well.

One of the design differences that I've noticed is the addition of a cylindrical section at the front of the float bowl, also the APT is adjustable from above... and the obvious addition of way more vacuum ports than I need.

The thing I'm wondering is; Is there any advantage to the later design that would apply in my own situation?
There seems to be more travel to the APT adjustment and I was thinking that may be helpful if I go into higher altitude which is less than 1 hr away.

Thanks for any and all replys and for being there to help out .

[Cliff Ruggles]

The later Q-jets with the APT system in front of the power piston accessible thru the airhorn are superior to all early designs.

They will also convert to electric choke which is typically required unless you have an early intake, divorced choke and matching carburetor.

Chevy Q-jets and divorced chokes came in several different variety in early years of production so can be confusing and difficult to locate and match up the correct parts for a working choke.

I consider a choke a must on anything street driven, same thing with a vacuum advance.  If it's going to see some street driving you need both.

There is a chapter in my book on carburetor selection.  My vote goes to the 1976 and later Q-jets (non-CCC) every time.  They are just better made castings with improvements to them in several areas, and most will be the larger CFM castings........Cliff

[rajon]

Thanks Cliff
I have just rebuilt one of the earlier units, just because I'm more familiar with those. But since I have one of the later ones too, I'll shift my attention to that.
I like the electric choke plan as well.

That brings up another question; How much warpage is tolerable along the front?
It seems like they're all warped.

I probably ought to get your book. I have the Fischer/Roe book but it doesn't mention anything about warpage or later design Quadrajets.

Thanks

[Cliff Ruggles]

Hopefully you ordered one of our kits for the rebuild.

All of them will have a little warping going on and it is NOT a big deal.  The big deal is how well the parts fit each other.

99.99 percent of the time using one of our kits with the .015" thicker top gaskets takes care of any problems in fit between the parts. 

A few seconds on the belt sander with the airhorn to make it slightly flatter than the main casting works for the other .01 percent.......Cliff

[rajon]

I had a quadrajet kit left over from when I last ran that carb, so I didn't need to order anything.
It seems to be working okay - but not optimal.
I'll take a look at the later designs and see which one seems the most serviceable, and order a kit.
I'm glad to have found you. I found a guy on ebay who sells parts, but minimal tech support.
I ordered some jets from him, but I'll be getting stuff here in the future.

Thanks - Bert

[Cliff Ruggles]

Good success starts with good parts and the correct parts. 

Most of the jets being sold aren't even for Q-jets but I'm not going into great detail there just to help out the folks selling the incorrect ones.

We have spent a lot of time and funds having better parts made and supplying high performance parts for these carburetors.

Even so folks still "google" and source out the cheapest parts they can find, then we get calls to the shop, emails, and threads running on here when they don't get good results.

So we try to get involved and get them better rebuild parts, and correct tuning parts for what they are doing.  Been doing this now for almost 20 years and most folks are successful with their Q-jets after we step in and help them out some.

The other basics to cover with all builds is to pressure test the bottom plugs and check side play at the primary shaft.  Leaking plugs or excessive wear in the throttle body results in poor idle quality, hard starting when cold (fuel bowl empty), and often very rich at idle when the front plugs are allowing fuel to be sucked directly into the intake.

Most carbs show a little warping but this is seldom a problem as mentioned.

For custom units we select the later cores as they don't have bottom plug leak issues for the most part, convert easily to E-choke, and you just can't beat the APT system for custom tuning them without having to pull the top and change parts........Cliff

[rajon]

I understand. For some reason I was thinking I'd be getting genuine parts. That's a bad assumption in this modern age.
I'll be a customer in the near future.

[matt68gs400]

The book will pay for itself over and over and over.  It