These had tons of troubles with intake manifold to head sealing and carb problems common. Carbon build up could account for high compression which with high load will knock.
Spray all around carb base and intake manifold for vacuum leaks. Generally when running ok - a good hwy run will clear out carbon build up,
T
Tom Greenleaf - MetroWest Boston - USA
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http://www.autoacsystems.com/tomgreenleaf/