When the car is run hard, out on the highway after getting home there seems to be a very loud knocking from the engine. I know when i was searching it down i loosened the nut on the air cleaner (i had tightened it) and the knocking stopped completely. I have replaced the spark plugs, i put in the factory spec ones (according to my motors manual for 1970 that i have) and that is an R-45 S and the ones that were in there were R-46, would this contribute to this at all? Why would they have put the R-46 in the car?

 

Check simple things like anything loose. One time my points were out of spec and the engine made a "knocking" sound.

AC 46 plugs are just 1 heat range hotter than 45. The 45 plug might have fouled and the previous owner went to the 46.

 

So I know this post is old, but I finally just found the source of my "noise"! I have tried so many things to fix this "problem" and nothing has worked. I was randomly under the hood today to work on something and started the car, then found the noise by accident. I noticed on the snorkel that the little peg going through was vibrating in time with the knock, it turns out this pin holds the spring loaded valve on the snorkel, and when I help onto it, the noise immediately stopped, and stayed stop while I held it, and started again when I let go. Now, just need to know how to fix this one.

 

I thought you found your problem when you loosened the aircleaner when you origanally posted this. Well the good news it's nothing major/

 

From the sounds of it,
1. the snorkel spring assembly welds have come loose - try tack welding them down?
2. the vacuum control motor may be shot. You can buy new ones and tack weld them in. When you search for this part use the search "Air Cleaner Heat Diaphragm"