I have a 350L48 engine that is forcing compression up thru the 4barrel. Any suggestions as to whats wrong are appreciated. The ignition timing is OK.

Bad intake valve or broken valve spring. If you have an HEI distributor it is possible that the module is bad and firing at the wrong time. I have had this happen.

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Steve Strasemeier (70SS 396, Fathom Blue/White Stripes)

The last time I saw this happen, it was caused by a flat exhaust lobe on the camshaft. Exhaust valve does not open so compression goes back out the intake valve when it opens. Try running the engine with the valve covers off (messy) and watch the rocker arms for proper action.

Bob Murray

Have you pulled the valve covers? I'd say, one of the above or a Broken rocker arm?? GT

shark
i would look at a broken rocker, or the famous rounded cam lobe.
67rat member#199