Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

17057266 1977 W72 q-jet- changes necessary?

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Mr Hand:
one correction: mechanical advance was set up at 20 degrees not 24.

Cliff Ruggles:
Without a positive stop welded in place and lighter springs to bring all the timing in early the HEI can and will add additional timing at high RPM's. 

With your application I'm not sure you'd get up that high, but ALL HEI's need a positive stop in them.

For your "low" compression build it still needs a lot of timing from the VA, so a 10 degree can may not be the best choice for it.

It is NOT lean if it works well.  The plugs should be light tan to nearly white.  If it's lean on the primary side the engine will surge, ping, lackluster power, poor throttle response etc. 

We NEVER tune carbs in this business by reading spark plugs.

For sure you need more fuel at WOT.  The factory DB rods have huge tips.  I'd get a set of our DA rods and if you want more control with the primary side fuel so you don't have to raise the APT clear up out of the bore get my custom full taper 45 rods at the same time........Cliff

Mr Hand:
thanks cliff I will look into ordering them.........I recall a post of your at PY showing how to add a stop. Do you mean adding it to the mechanical advance or the vacuum? , I will try to find it unless you have a link or something?

Cliff Ruggles:
We add a positive stop to the mechanical advance in the HEI. 

The factory designed the HEI to stop advancing when the "flats" on the weights reached the "flats" on the center cam.  It does OK with the stock spring but IF you install lighter springs the weights can and will "roll-out" on the tips and continue to add timing at high RPM's.

Installing a positive stop is NOT an option, they all do it and I'm sure plenty of engines have had the rod bearings pounded out of them from detonation at WOT because folks trust those cheap POS spring weight kits or the folks who install lighter springs with their stock parts.....FWIW.....

Cliff Ruggles:
I also modify the VA cans if/as needed to add exactly how much timing I'm wanting.  I use VA cans with the spring tension I'm looking for (start/stop points), then simply MIG weld the slot and "adjust" the amount of travel with a round chainsaw file.  Pretty easy stuff there, and no need to have more than one VA, I can put it where it needs to be for the application........

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