340 Pinging using 94
Tbh, I have no idea how lower octane will help reduce it
It is what my mechanic recommended
Your mechanic recommended?? I recommend trading him in for a different model. He should first be looking at the plugs to see if it is one cylinder or all.
As Rusty suggested, a vacuum leak can cause detonation and finding a vacuum.leak is fairly simple with an unlit propane torch. Turn the propane on and direct to the intake gaskets, carb base gasket and vacuum hoses. If the idle changes that is most likely the vacuum leak.
Considering this just started, the possibility of fuel could be possible, but only if high compression was built into the engine. Octane boosters are a bandaid for your real problem. Again pointing the finger at your mechanic, he should have the tools and knowledge to check the advance curve. Rusty could be correct on a broken advance spring.
Another consideration could be a bit of carbon getting hot in a cylinder or two, igniting the mix early.
New to the hobby, eh. I would find a local car club and get to know the people. Every club has people that are good with body work, interior, engines, paint and other components. Many times you can swap time in your talents for time in theirs. And that does not necessarily have to be automotive related. Some have bartered body work or a differential overhaul for getting a deck built. You meet some nice people and save some of that hard earned cash that the left dishonourable prime peckerhead of Canada, daesh dustbin turdo is fervently making harder to come by and to keep.