Hey guys. I'm new to this and this is my first Monte Carlo.
I own a 1987 Monte Carlo SS Aerocoupe, has the stock 305 engine.

I love the car its just that I have many questions about it still.

The previous owner said he'd put 91/93 octane gas in the engine. I didn't think it would need that as it's the stock engine and not a performance engine such as a 350 or so you know? Well that's what I read anyways. So I've been

putting mid grade fuel in it since I got her. And at first she seemed to like it enough but over time I noticed that when I'd crank her up she'd start knocking. And I kind of knew it was the fuel type I was putting in. But I'd continue to put in the mid grade fuel, somehow hoping it would get used to that instead of the high octane fuel. But it has gotten worse. She still cranks, but I can hear it getting louder, last time I filled her up I put in the high octane fuel....
and she did seem to even drive better with that fuel. It was a better drive for sure.
but the engine still knocked at the crank.

My question is what do I do about the knocking? Did I already completely mess it up? Do I Take it to a shop? Or can I wait it out and keep feeding it high octane and she'll go back to normal?

side notes: she also needs a tune up, and the carburetor chokes. But I didn't have the engine knocking until I filled it with mid grade fuel. So as I know these may also be linked to it, im almost positive its because of the fuel type.

maybe it's a stupid question? I don't know.

thanks in advance

 

You might need to time the engine, carbs do need to be messed with every now and then.

 

Sometimes a fuel additive will help like Lucas fuel injector/carb cleaner.
You might want to experiment with the place you get gas also maybe the fuel mix is better at XYZ station that ABC station. There might be some better fuel additives to pick as well.