So I've had my 73 c20 for a couple of weeks now and I've known something was off with the timing. Anyway long story short , I checked it today. Plugged distr. vac. did not adjust throttle. Found timing mark. Hooked up timing light that has knob to set the amount of advance you want to 0...no mark. Slowly turned knob... timing mark was at 0 on plate...30 on light. Am I doing a whole lot wrong, or is there a whole lot wrong with my engine?