pre-detonation for '40 LaSalle

[Warner15]

My '40 LaSalle developed a knock (pre-detonation) in September.  I've added lead substitute to the gas and mixed about 30% premium gas, but have not cured the problem.  I drove the car for 9 years without this problem.  I have used lead substitute often in the past, but not every tank.
I've run out of things to try.

[wheikkila]

My first thought is a issue with the distributor. I would check the points plate. They have three balls that allow the plate to rotate. It could be it is staying in the full advanced position. or more. Next check the timing it may have jumped. Because these engines are very low compression. You should be able to run low octane fuel without issues.   
              Thanks Wayne

[James Landi]

Agree with Wayne--- also, you should be able to move the rotor (in the distributor) by hand-- perhaps 1/2 an inch and it should SPRING back...if it;s stuck or won't spring back, there's a problem.  ALso, check the timing with a timing light. (DO these cars have vacuum advances???)  Something is causing the timing to be off, and it's apparently not the gasoline mix.  Hope this helps to generate more comments.  James

[wheikkila]

The car should have a vacuum advance. If they go bad normally they don't advance the timing. A trick to use your timing light is to bring a 12 volt battery close to operate your timing light. Please be sure to let us know what you find.
                   Thanks Wayne