my tach runs up to 4k at the turn of the key to "run", no starter yet, engine not running. Once running tach rolls up to 8k and stays there as long as engine is running. When engine is turned off, back to 0. It has done this since I bought it. I've added a Pertronix ignition and a 4 barrel carb setup which has improved driveability, but did not affect tach issue. Any ideas?