Sometimes, a carbon knock will sound just like a rod knock. It will
sound like it's ready to throw a rod. I can't even count how many times
I have fixed this with about half a bottle of transmission fluid.
Start the engine; remove the air cleaner; rev the engine up to about
2500 rpm and start slowly pouring the transmission fluid down the
carburetor throat. Don't let the engine die. (if it does, you might
have to pull & clean the plugs, then resume the procedure). Pour the
xmf fast enough to lug the engine down.
Voila -- no more knock. Gone for good. This apparently happens when a
little piece of carbon breaks off inside one of the cylinders or
something..... but I've fixed 'em numerous times this way when I thought
I had lost a rod bearing.
--Brooks in Dallas
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