Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

17057253 carb not idling or revving

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Seff:
Running an aftermarket HEI, it has mech and vac advance. If I turn the dist in either direction any considerable amount, idle drops and/ior becomes choppy. Don't have a tach, so I don't know how high it's running.

Seff:
It was running 50 degrees at idle, so I took it down to proper levels and the carb runs much better. Needs dialing in once I get back to my actual workshop, including tip-in. Maybe I'll get above that 14 MPG I've been getting so far. :P

Cliff Ruggles:
Initial timing MUST be set at idle speed with the vacuum advance unhooked and line plugged.  Also verify that the mechanical advance is NOT adding any timing at idle speed.  Base timing for most engines will be around 8-12 degrees.

The HEI may add a LOT of timing at idle if a manifold vacuum source is used to apply it.  This will increase engine rpm's, and may cause difficulty in setting the idle speed at normal rpm's.

I use and recommend ported vacuum for most set-ups.  Using manifold vacuum often requires that the advance be modified so it doesn't add a lot of timing at idle speed.

For most well thought out engine combinations, we limit the advance unit to 10-14 degrees, and almost always apply it with a ported source.....Cliff

Seff:
Currently the HEI vacuum is connected to the DVCS.

Seff:
Is it better to use the DVCS or to use ported vacuum? I have a spare ported vacuum port left over from the secondary choke pulloff.

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