Q-Jet to Edelbrock carb swap - linkage question

[Grit dog]

Yep, I thought of the 180 degree out idea, that wasn't it, either. Yes, it ran before swapping the carb and pulling the distributor, but it dieseled when shutting it down, leading me to believe that either the timing was already a little off or the Q-jet carb needed work, which is why I tried swapping the carb in the first place. Or vacuum leaks, which I checked thoroughly. I feel a little better, because I took it to the local shop that works on these old birds a lot, and they are having the same trouble. They got it to run with the Eddy on it, but it still behaves like it has a massive vaccuum leak, but they can't find any either. Maybe 600 cfm just isn't enough volume and it's just too damn lean? I could change the jets and metering rods to the largest flow possible, but it would be simpler to just use the old Q-jet again. I was hoping to improve my fuel mileage a bit with the Eddy.

Did they hook up a vac gauge?
Since you’re pretty confident on timing, As quick as it is to swap a carb I’d think about un repairing the carb toss the q jet on and see if it runs.
Also did you actually base time it with timing marks or cranking the engine with a timing light? A tooth off could make it not start or barely start.
Just spitballing.

 

[Grit dog]

Rebuild kits for the Qjet are easily had.
Take your time and clean it up. Rebuild it.
I love my qjet so much, I have a twin for just in case.

Get Cliff's book on rebuilding qjets.

Been so long since I drove something with a q jet I don’t recall them being special. I also don’t really ever recall carb issues on a pile of 70s-80s GM small and big blocks in the family and at work where it was my high school job to fix them.
Las time I drove a square or anything with a carbed GM V8 was 25 years ago and it was my 2bbl 400 Impala….until getting the K20 5 years ago. It and the 77 came with good working Edelbrock carbs but they don’t seem quite as seamless as I recall all the old Qjet vehicles back in the day.

 

[BigT]

600 cfm on a stock (or stockish) small block is plenty, in some instances probably still more than it needs.

Carburetor CFM doesn't work on the more is better principle. A smaller carburetor will be more tuneable and responsive to tuning than a larger one on the same engine. Say a 1050 dominator vs 600 holley on a stock 350, the 1050 might make a little more on a dyno but will have poor street manners. Basically there isn't enough vacuum signal at idle/low rpm to properly meter the fuel, typically an oversized carb will bias to lean as it cannot pull the fuel correctly. You'll fight it forever.

A smaller carb, say a 390 vs a 600 will make less on the top end, but will have excellent vacuum signal and will meter the fuel properly and react well to adjustments.

All this to say, a 600cfm carb is perfectly fine and size isn't the issue here.

If it dieseled before with the Quadrajet, there is a fair chance that the timing was too retarded and required more idle screw to get the rpms up, which opens the throttle plates and makes it idle on the transition circuits, not the idle circuit, which makes the idle mixture screws ineffective. Which also leads to dieseling. Timing should really be used to set idle speed, not the idle speed screw (it can be used for small adjustments).

Remember, carburetors are pretty forgiving, ignition is not. And a majority of fuel issues turn out to be ignition problems.

Very good thoughts, thank you!! I was pretty sure the Eddy carb was not the issue, so it's good to see this. Makes me feel a little better about my instincts.

Is the egr hooked up? Wondering if you have egr plumbed to manifold vacuum,which could definitely would trip you up.

Good question. I believe it is connected correctly, but I will have another look this evening and verify.