Hello all I am new to forum. I have a 70 supreme conv with a 350 4spd and #5 heads. It sat for 20 years then I flushed all fluids oiled it up. It had no spark so I decided to go the petronix route and it fired right up. Now i have been driving it for a couple months and it has always had a knock at about 1800 rpm to 3000.rpm. when I disconnect the advance hose it goes away a little which leads me to believe it is spark knock. Everything is original except the carb which is edelbrock and petronix ignitor and coil. I used the champion plugs. Timing was set by mechanic and it runs smooth just the knocking during acceleration. Could the springs be weak for mech advance or vacum canister for advance pulling early? What are some trouble shooting I should be using?

Thanks.

 

I would use a dial back timing light or a marked balancer to determine what the total advance is and at what RPM it is coming in, and also check the amount of vacuum advance. You can use the springs from an advance curve kit to tailor the rate the mechanical advance comes in once you know what's going on with the current setup.


Oh, I guess I should ask what octane gas are you using. Too low octane is easy to correct by switching to the highest octane available.

 

Thanks for the reply! I use only 94 or 91 try to find no ethonal when I can tried octane boosters but same knock. I am going to see what my total advance is with and without vac and try the recurve kit. It is smooth at 60 mile an hour and has power but around town I get the knock.

 

It seems your timing is set wrong and look forward to find out what the current settings are. Need to know what your initial is at idle with and without vacuum advance and what the total is with and without vacuum advance and at what RPM it actually stops advancing. You may have to rev to 4-4500.