Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

Idles great, dies when I drop into gear

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von:
It can also be caused by the particular vacuum advance can being used with full manifold vacuum. I had a '70 L78 Nova with TH400 that had this problem when the vac advance was connected directly to full manifold vacuum. To maintain correct idle speed in drive, it would idle way too high in park/neutral. Adjust idle speed down to correct in park/neutral and it would die when put in gear. Disconnect the vacuum advance or connect to port vacuum and the problem went away. The "activaton point" of the vac can was evidently where it would provide advance with the manifold vacuum the engine had when not under any load, but when put in gear it was enough of a load (with the L78 cam) to reduce manifold vacuum enough to take away enough advance to kill the engine.

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