Thanks Steve

10 hours ago, Patcon said:

Any thoughts on coil temp?

We put 50w in the carbs. It did not make it rich enough. Very little change. We may try a really heavy oil to verify that that is all the enrichment heavier oil is going to get us.

We also have a problem with "running on" when shutting down. May actually be running in reverse. What causes that?

Way back when I was in high school in the late 1960's, my parents owned a Volvo 142S that would do the same thing. It's known as 'dieseling', 'run-on', 'auto-ignition', or 'after-run'. Our Volvo's engine (a 1.8L four, with twin SU's and a remarkably high 10.5:1 compression ratio) would run happily in reverse for 15 seconds or more after the ignition was turned off. Sometimes it would run smoothly, other times it felt like it was going to shake itself to bits. The only way to get it to stop was to put the car in gear, apply the brakes, and then let out the clutch until the engine bogged.

Dieseling occurs when there's an ultra-hot spot somewhere on the surface of the combustion chamber (or chambers). They act like rogue spark plugs and can usually be traced to red-hot carbon deposits (common in older, carbureted engines b/c they run relatively rich, burn dirtier, and accumulate carbon quickly). Under these circumstances, it seems that even a half-millimeter throttle plate gap will allow enough airflow to let the engine keep turning. It's been suggested that worn throttle shaft bushings contribute to this.

Don't ask me how an engine decides to run in reverse at the start of this process.

Maybe your 510's engine has got carboned up during your start-up testing?

11 hours ago, Patcon said:

Any thoughts on coil temp?

We put 50w in the carbs. It did not make it rich enough. Very little change. We may try a really heavy oil to verify that that is all the enrichment heavier oil is going to get us.

We also have a problem with "running on" when shutting down. May actually be running in reverse. What causes that?

Yes, we have been very rich. It's possible it's carboned up. We'll have to work on that too