03-06-2021, 04:11 PM
If the tappet screws are indented you'll always struggle to gap them correctly. However, I wouldn't worry too much if it is a bit 'tappety' at the moment. You can sort that later once you've got the engine running nicely. As a very experienced motor engineer known to a few of us on hear often says, 'You can't hear a tight tappet'! As to the rumbling I agree with the suggestions above, sounds like too much advance.
Steve
Steve