General Category > Quadrajet Carb Talk and Tips

'66 calibration data

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ourkid2000:
Thanks Cliff, I have your book and am trying to find the best path forward. I guess I have two options available:

1. Just find a service replacement for the '66 7026250. Rochester produced the 7041312 service replacement for the '66 in the early 70's that has many of the original issues dealt with. That would be except for the secondary air valve damper which still used the original design for some reason. These aren't easy to find.

2. Your book recommends a '76 or later M4M carb as a substitution. I'd have to find one with a side fuel inlet and an electric choke along with a ported spark vacuum line and a straight vacuum connection for the transmission modulator. In addition I'd have to get the original throttle linkage welded onto the primary shaft as they are different lengths from what I understand. Then, I'd have to rebuild the carb to work with my bone stock original engine (~385 gross HP). Maybe something along recipe #1 lines?

ourkid2000:
I found myself a nice set of precision drills and figured I'd try my hand at measuring the carb myself. Here's what I got, if anyone knows if these are accurate for a 7036250 (or 7026250) please let me know:

Main Air Bleeds:
Air horn = .039"
Main body = .055"

Idle Air Bleeds:
upper = .041"
lower = .067"

Downchannel restriction = .037"

Idle tube end restriction = .039"

Idle discharge holes = .0785"

Did I miss any? Thanks!

Kenth:
Here is what i have on the #7026250:

ourkid2000:

--- Quote from: Kenth on January 17, 2025, 08:27:08 AM ---Here is what i have on the #7026250:

--- End quote ---

Wow thanks Kenth! That's awesome. It looks like mine has been played with a bit because my idle tubes at the small restriction are way bigger than .030. It was rebuilt at one time, I bet they pulled them and replaced with whatever they had on hand.

Everything else looks pretty close (any errors probably lies within the tolerances of my somewhat cheap twist drills). Mine being an emissions carb (703), I'm thinking it is just calibrated a little leaner than the 7026250.

But thanks again, what a resource!

novadude:
Just a curiosity question... are upper idle bleeds in the airhorn on this carb?  I've never seen upper idle bleeds in the float bowl that small.  Thanks!

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