4Cruisers
SILVER Star
Is your '78 a Federal spec vehicle or California spec? The '78 California spec distributor only has a retard port, the Federal spec has two ports - advance and retard - one on either side of the diaphragm.
On your mechanical advance, there's a small bushing over the stop pin that limits the maximum mechanical advance. They are usually toast unless they've been replaced. If it's missing, the maximum advance will be greater than spec, which could lead to pinging under load. It's easy to replace - clean the stop pin (under the breaker plate assembly) and push on a nylon or aluminum bushing. The proper size is 1/4" diameter X 1/4" long, for a #8 screw. Easy to find at any decent hardware store. That could be contributing to your issue.
On your mechanical advance, there's a small bushing over the stop pin that limits the maximum mechanical advance. They are usually toast unless they've been replaced. If it's missing, the maximum advance will be greater than spec, which could lead to pinging under load. It's easy to replace - clean the stop pin (under the breaker plate assembly) and push on a nylon or aluminum bushing. The proper size is 1/4" diameter X 1/4" long, for a #8 screw. Easy to find at any decent hardware store. That could be contributing to your issue.