I seem to remember a procedure for centering the jets. i rebuilt mine some 20 years ago, so I sort of forget..its probably like a nut that frees the jet up .. I wondered if maybe someone trying to adjust them could have simply loosened it and maybe not realized that the jet needed to be aligned to the needle, thus maybe making the needle rub on the edge of the Jet's orifice.

if the PCV hose is hooked up to barf fumes into the air cleaner the pistons might get dirty from the regurgitated smog. I should probably take mine apart to clean, but they work fine. If I recall right the 66 had a connection to the manifold and in 67 it wen to a thicker air cleaner with a PCV hose to
make the air cleaners dirty. very early ones may have had a ground tube or similar. I think older cars, like around 62 and earlier may barf that crap on the ground. motorcyclists won't love that.