Mth 30-4049-1 blue comet "quirks."

Your engine is not receiving a tach signal.  So either the tach reader is bad, the stripe is bad, the gap is bad, the wiring in the engine is bad, the wiring in the tether is bad, or the Power Supply has a bad speed control chip.  You can see if the 3 wires to the tach reader are connected and the cleanliness and gap of the read.  After that the trouble shooting is a little more involved unless you understand how the engine is wired.  G