Sorry, the tach signal comes from an engine management module. I plan to use a position servo as a kind of govoner. Basicaly I need to hold the engine speed constant over a varying load. The current govoner uses oil pressure to move an arm to control the throttle, this is adequate if the load is fairly constant. unfortunately this is not true in my experiment.
What i have been trying to do so far is to make a servo follow the adc. so far its not working right, but that could be because the code is still sloppy. I do not write in C yet, still tinkering in assembler. And the costs out weigh the benifits that basic provides.