Ive recently cleaned the burners on a 1964 homart 600 series nat. Gas boiler and when finished noticed the flames from the burner were running what appeared to me as being too high. Just about up to the cast iron and burning yellow. No change in color with the adjustment of the air flow damper. So I found that if I turned the ( off, pilot, on control knob back a little bit it would slow the gas supply down and bring the flames down to about half the height where I could adj. The damper and get a nice blue flame. My question is, is that pilot control knob made for variable pressure or volume like that or is it meant to be turned to the completely on position where the flames will be 10 inches high or so. Thanks

Normally the gas valve is left to the full "ON" position. I suggest you have things checked by a local professional.