Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Full throttle knock, jet help

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77cruiser:
How much total timing? Vortec heads like about 32, I think swirl port heads less maybe 28.

cj7:
its 9.6:1 cam specs are Camshaft: Hydraulic roller Cam Duration @ .050 in.: Intake 191 / Exhaust 194 Cam Lift: Intake 0.414 in. / Exhaust 0.428 in. Lobe Separation Angle: 112 lsa. total timing is 29 degrees. but according to your book and the recipe for success, the jet should be 71-76, so 60s seem low

Cliff Ruggles:
You are working with a single main airbleed carb, so the "recipe" for success woln't be the same as it would for an earlier Chevy model with two pairs of MAB's.

Those are the first SMAB units and only used in 1977 and 1978 in the divorced choke truck units......Cliff

cj7:
in one of the notes, it states the later SMAB units bigger jets 74-76. if not, what do you recommend for jets, and primary and secondary metering rods? ive got a few laying around, the rest ill need to order from you

Cliff Ruggles:
The model you are working on is referenced on page 98 stating that they used smaller jets/metering rods, still used the early casting design, etc.

I don't use or recommend putting used jets in any carburetor one is building or tuning.  They will seldom pass a pin gauge test (worn internally from the metering rods sliding up/down in them).

When you are ready for tuning parts, let us know, and using the APT system in the baseplate you can fine tune on the vehicle without having to take the carb back apart......Cliff

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