If you suspect the timing tab is inaccurate, the first item of business is to check it. Make a "positive stop" device from an old spark plug shell and a bolt, install it into the #1 or #6 cylinder, and and slowly rotate the engine until the piston touches the stop bolt. Mark the damper at the zero point on the tab. Rotate the other way until the stop is reached. Mark again. TDC will be exactly halfway between the two marks. Now, with a known accurate TDC mark, you can set the timing properly. Just like the slogan on Sun Electric Co. machines used to say- - - -"We Test- - - -Not Guess!"
Jerry
