Q-Jet to Edelbrock carb swap - linkage question

[BigT]

Swapping out my old worn-out Q-jet on my 350 with an Edelbrock 1406 I already had, but the accelerator linkage setup is different, see pics. First is the Eddy, second is the stock Q-Jet. Isn't there supposed to be a stud sticking out on the Eddy to connect the cable end to? It's also got a bent tab, I know, but none of that mattered on my Chevelle, so I never worried about it. Anyway, I could use your thoughts on a fix. Thanks!

Tim

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[warrpath4x4]

Theres an adapter needed

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[Chevy 88]

I did the same swap on my rig. Same carbs.

As a temporary solution just to get it on the road - here is what I did:

 

[BigT]

Thank you! I'm off to O'Reilly's.....

 

[BigT]

Well, that fix worked well, thank you! Sadly, I can't get the old booger to start now. She just backfires through the carb. It's got to be a timing issue, but I've checked to make sure the wires are connected to the correct cylinders, set the rotor to point at #1 while at TDC, messed with the timing, etc. Everything I can think of, and no dice. I'm stumped and frustrated, so it might get towed to the local mechanic to sort it out. I'm burnt out.

T

 

[Grit dog]

Well, that fix worked well, thank you! Sadly, I can't get the old booger to start now. She just backfires through the carb. It's got to be a timing issue, but I've checked to make sure the wires are connected to the correct cylinders, set the rotor to point at #1 while at TDC, messed with the timing, etc. Everything I can think of, and no dice. I'm stumped and frustrated, so it might get towed to the local mechanic to sort it out. I'm burnt out.

T

But it ran before swapping carbs? Ran before figuring out the throttle cable?

 

[Chevy 88]

Popping through the carb can be caused by a carb issue.

 

[Ricko1966]

Was the distributor moved or removed during the carb swap. The distributor moves at 1/2 crank speed. What this means in this situation is when the timing marks on the crank line up,the distributor rotor doesn't necessarily point to 1 it could point to 6 and that wouldn't have been wrong. The rotor points to 1 if the intake andvexhaust valves on number 1 are both fully closed if 1 or the other valve is partially open the rotor points to 6.

 

[hey mister]

When she pops back thru the carb, it's most likely...Timing could be out 180°.

 

[Grit dog]

When she pops back thru the carb, it's most likely...Timing could be out 180°.

True story. But no back story to verify what the OP did or didn’t do….messed with timing….is all we got.
Fwiw, 17 year old me also learned that timing 180 deg out can and will also very effectively open up brand new turbo mufflers so you can see how they were constructed internally!

 

[BigT]

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.

 

[legopnuematic]

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.

 

[Ricko1966]

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

 

[hey mister]

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.

Excellent explanation.

 

[hey mister]

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.