cfair

In the early 80's, the original quadrajet on my 98 had worn out. At 17, with no one to teach me, an Olds engine compartment looked like a maze of mysterious wires and hoses. To make it run right, either I or my Dad had a local mechanic put a rebuilt qjet on.

For reference, 1966 was the first year for quadrajets. The early ones had a passenger side fuel inlet. My rebuilt was resealed with a freeze plug where the fuel does a 90 degree turn from the passenger side inlet to the needle & seat. Along the way, my rebuilt qjet freeze plug leaked gas onto a hot intake manifold causing an engine fire. It BBQ'd the engine harness and damaged other electrical parts. After a few months the car was back on the road with work from a local mechanic, but the fire damage wasn't really fixed until 5 or 10 years later when I installed an unhacked wiring harness. That fire memory stayed with me as I went along learning about cars

Eventually I learned that later quadrajets (75 & later M4MC aka the 170... series) changed the fuel inlet design. These later quadrajets take fuel in through the front of the carb, just behind the thermostat housing, not from the passenger side. This eliminated the need for a freeze plug. I suspect what really got my attention for the later quadrajet designs was the 800 cfm rating in combination with the safer fuel intake. But hey, more CFM & safer? Great!

Here's what a latter day quadrajet looks like installed:

1966 98 with 17058553 quadrajet, HEI, and hand made hardlines

If this idea attracts you too, there are at least a few caveats. Early 70 series and and later 170 series carb parts don't swap much. In fact this is so true, I gave all my 70 series parts to my regular mechanic since I didn't want to mix them up. Plus he could use them for other customers. Win-win. The 170 series quadrajets, despite some having 800 cfm rating, vs the 70 series 750 cfm rating were most commonly found on smaller displacement engines with lean rods and jets.

If you acquire one from a boneyard, you'll need to swap jets & rods to use it on a 400, 425 or 455. Right now I'm generally using 74 jets and 44 rods on the primary side. This combo works pretty well, but it's a tad on the rich side. I'm still experimenting to get it just right. Also be aware the later carbs are from the emissions era just before the computer controlled qjets, so if you grab an original from the boneyard, the idle screws may be hidden and the whole thing vis a vis airbleeds, and other circuits are tuned for lower emissions, not power. I'm not affiliated, but have gotten good quality rebuilt carbs from SMI in Huntington Beach, CA. I'm also partial to quadrajets.com for replacement gaskets and other small parts.

There are books on quadrajets, best being the ones from Doug Roe and Cliff Ruggles, so I won't cover that here, but maybe this helps some of you find a good starting point to make your cars safer and more powerful at the cost of being not quite factory and a major investment of time.

Some of you may notice non-factory hardlines here. I wanted to learn how to bend 'em a while back, having had the tools for decades, but never really learning what to do with them. I may return to rubber one day, but for now I kind of like the industrial look and function. The downside of bent metal tubes is I'm increasing the number of connection points, aka potential vacuum leaks. Having said that I was happy to get a metal fuel line back in place between the carb and fuel pump. Feels better and safer than all that rubber in our time of ethanol fuels.

Hope this helps some of you as you have all helped me.
Chris

cfair

I forgot a biggie here. The later qjet has a riveted throttle cable connection, not a throttle rod connection hole like they used in 1966.

I just used a dremel to grind and knock out the bump/boss/rivet for the cable connection and popped it out. This makes room for a 1966 1/4" throttle rod with a bit of fiddling around with the right size bushings. Go softly if you do this because it's connected directly to the primary throttle blades and can cause a vacuum leak if you gorilla handle it.

Also only dremel the throttle plate in a safe location away from fuel since it'll create sparks for sure. Like away from the fuel bowl, with the carb off the car and empty.

Since I change my qjet setup fairly frequently note that I secure my throttle rod with an easily removed hinge clip, not the proper cotter pin.

Sorry to leave this out

Chris