I have a 65 with the 230 also. I was having a good bit of spark knock, especially when giving it a little gas while cruising along at about 55 MPH. Carb adjusted, and I have been using a lead substitute in my gas tank. I took it by my mechanic buddy's garage, and the timing was only off slightly, which he fixed. Still had a bit of spark knock.
I took it back by and he gave me a can of GM Top Engine treatment/cleaner. Poured about half the can down the carb, keeping it running, then increased the flow until it shut off. Let it sit for about an hour, cranked it back up, then finished off the can. Lots of smoke starting back up, a trip down the highway to "blow it out," and no more spark knock.
Maybe a similar treatment will help you out. By the way, he has been a mechanic for about 30 years, and said that the GM cleaner was the best he has tried. The only brand he keeps in stock now.
Mike
