My 235 has been running poorly lately. Doesn't seem to be electrical, changed plug wires etc, no vacuum leaks, has a holley weber 2 barrel. My vacuum gauge really bounces and the reading is between 15 and 18 inches. I was told this usually means a valve train problem. The lifters and rockers all seem fine with engine running,just reset the gaps, so the cam is fine.. So does this mean I have a bad Valve? The engine was rebuilt about 1500 miles ago.