Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
Idle Speed Issue
Zach:
Howdy, everything is bone stock besides a fresh SR rebuild kit from Cliff in the Quadrajet #17057263.
The carburetor is the original one sitting on top of a stock 1977 Pontiac 400 W72 (think it has a better cam and slightly more compression compared to a stock 400). My current issue is that in order to get the target idle RPM of 775 it requires me to almost completely unscrew the curb idle screw which I assume is where my slight hesitation on and off the accelerator comes from since there is almost no transfer slot seen. The initial timing for a Pontiac 400 is 18 degrees, which is high compared to most and this means my idle is gonna be higher as well, I have tried a more tame 8-12 initial with the carburetor transfer slots properly visible, however, there is a lack of power once I get on it, most likely due to total timing being low.
Car is running absolutely flawless besides this very very slight hesitation, just wondering on some solutions to this issue. 19 with very little experience with all this so I am just learning as I go. Should state there shouldn't be any vacuum leaks, went over everything + cliff installed new bushings.
Cliff Ruggles:
Higher compression might be a player here. Those engine used a LOT of initial timing because the compression ratio was really low and not squeezing things very hard at idle speed. If you retard the timing the engine will certainly idle slower, but you'll have to modify the advance curve so it still gets enough total timing to make best power......
Zach:
--- Quote from: Cliff Ruggles on May 04, 2023, 07:54:08 PM ---Higher compression might be a player here. Those engine used a LOT of initial timing because the compression ratio was really low and not squeezing things very hard at idle speed. If you retard the timing the engine will certainly idle slower, but you'll have to modify the advance curve so it still gets enough total timing to make best power......
--- End quote ---
Ok, figured the solution was to change the curves just wanted to see what you guys had to say, thanks.
Guess I will start researching, got any good resources for proper timing procedures? I assume I will square off the transfer slots and then retard timing till idle is where it should be and consider that where my initial should be. Then I just have to find the right springs and weights for HEI and swap them. Will I need to swap vac can at all? It’s running off emission timed manifold vacuum (mimics ported) or can I get by with just messing with mechanical. Thanks again, wouldn’t survive without these forums, learned a lot from them.
Cliff Ruggles:
The stock weights, center cam and springs are fine, you just need to modify the advance curve by adding a positive stop to provide the amount of timing needed. I use a MIG welder here to weld up the slot and round file to open it up. Timing is measured using a degree wheel. 10 degrees at the distributor is 20 degrees at the crank, etc.....
novadude:
That pointer and degree wheel is a fantastic idea for setting total centrifugal!
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