I've had my 64 Skylark, since I was 17 in the late 60's. The pic was of a completed restoration in 87, due to career demands and nationwide travel, I had to mothball it in the garage. We recently replaced all of the ignition, components on the Fireball, also water pump, motor mounts, cleaned out the Rochester BC, coolant, oil filter and of course new oil... We drove it about at low speed numerous times. On the driveway it began to "miss" like a plug was fouled.. So I reved et up a little and it became worse.. I checked the plugs they were all still clean.. I checked the position of the Dist, so see if it had moved and threw the timing off, even though we never had to adjust the timing, the fuel filters were ok, fuel pump ok.....
.. The only thing left ?? the (lifters, push rod rocker arms assembly).. after pulling the intake we found four of the twelve push rods were partially bent about 1/2 inch. Since this is a "Non interference engine " we had no further damage. After doing some research I found that the hydraulic lifters tend to contain some oil, which over time degrades into a varnish like gum. SO four my lifters seized up, and bent the push rods. My 1964 chassis service manual, details how to disassemble clean and reassemble the lifters, that's how they did it back then.
I pulled both rocker arms and soaked them seperately in mineral spirits, to clean out the oil passages, that haven't been cleaned out since this 1967 engine was transplanted into my 64. It took several soakings of the rocker arms, before the solution remained clear, showing that all of the particulate matter was flushed. I ordered / installed new Melling Brand, hydraulic lifters and push rods, also the intake manifold gasket. (while the OEM intake was off, we replaced it with an Offenhauser 360 Evenflow performance intake, fitted with a Holley 390 cfm, 4bbl.
Back to the Hydraulic lifters. My research online found that one can perform an engine flush using a mixture of new engine oil combined with Marvel Mystery Oil. Had I thought of It, I would have dropped the oil pan to give it a through cleaning. A lot of oil that does not fully drain out, pools up and remains on the bottom of the oil pan where it gets cooked up and resembles a black tar like matter. Also I changed out the rubber fuel line, from the gas tank to the steel fuel line. That hose segment was about 1/2 blocked with a black tar like substance. I don't know how the 1 bbl got enough to run ! A mechanic told me that's how gasoline breaks down. I also replaced the forward segment of the fuel line hose where it's positioned close to the mechanical fuel pump, and of course from the fuel pump to the carb. If you are not comfortable re the above, consult a "reliable, honest, knowledgable" mechanic.. Best Regards.