detonation / knock issue on 340

shimsham1 said
Hey all, trying to work out some issues on my 340. has bad detonation / igintion sounding knocking. i did not build or know anything much about the engine. Has a holley carb, mopar performance high rise intake. I've changed plugs, timing, fuel, etc. i noticed that when i spray carb cleaner at the base ( intake manifold ) gasket it wants to stall so i'm guessing bad seal there. does anyone have any other ideas for me to check where its coming from. its from idle to lie 3000 rpm then it goes away and the car runs and sounds like an animal. i did not change the plugs or cap. i got this car from someone that had it on jackstands for 19 years due to a bad trans , never starting it. i got the trans rebuilt and have just started driving and attempting to tune. any help would be greatly appreciated

With the engine being totally unknown to you, I would fix the carb gasket first since that one is an obvious issue.

I would test to see what the cranking cylinder pressure is. Too high and you will have to address it.

I would also turn the engine over to top dead center on #1 compression stroke and make certain the rotor button is pointed toward the lt front intake bolt to verify/ eliminate a timing or chain issue. Also need to check the harmonic balancer marks to ensure accuracy.

Make certain the advance weights in the distributor are free and lube them up.

Take the gas line loose coming out of the pump and fill a small glass jar to rule out rust in the tank causing a lean issue. I would also just go ahead and replace the filter. I am assuming you already pulled the tank and drained the old fuel.
Don't put more than 3 or 4 gallons back in in case the old scale inside turns loose with new gas as you don't want to have to deal with draining or dropping a full tank. Find some 93 octane if available in your area.

Once all that is done and any problems corrected then I would start trying to tune.