[Rev]

Put a vacuum gauge (any auto supply) on a manifold vacuum port. A stock 289 should show 15-17 in hg. vacuum. If it's a stock engine and it's alot less, then you do have avacuum leak.

A leak can occur at the head/intake manifold interface or at the intake manifold carb interface. Also a leak can occur in the carb itself where the butterfly shaft works in the carb body (loose fit from wear).

You pretty much need a vacuum gauge to diagnose the problem. For $30 it's not a bad deal. You'll need it over and over again anyway as the years go by.

Rev