Quote:
Originally Posted by 304065
Bob, try a 38% duty cycle or less-- 50% would be appropriate for 4-zyl- and use 11V.
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It works now, thank you. 304065
I have another tachometer which has a + , C, -. on a 914-6 project.
This unit runs with a 3 pin cdi. The C will be connected directly to the points on the distributor or to the C on the CDI?
The analog signal is a fast high signal (spike)when the points open the pulldown?
Br Bob
3. 1971-1973 Tachs. These appear the same externally but have been altered internally to be driven off the high-impedance circuit between the points and the Bosch CDI box. In the early 3-pin CDI boxes, there is a 33 ohm pullup resistor in the trigger circuit that would allow only around 425 mA to flow in the circuit. The tach must be sensitive to 11 volts and 425mA, which is why the later CDI won't drive the earlier tach off this circuit-- the earlier tach needs higher voltage.
4. 1974-1977 Tachs. I know these were driven off the CDI box, but I don't know when the CDI box changed from an "001" to an "008" or when the cutover from a 33 ohm pullup resistor to a 120 ohm occurred. With 120 ohms the input current is only 116mA so the tach must have changed somewhere along the line to match. If you send your tach to NH speedo to be recalibrated they want to know what CDI box you have, so this must affect the input value to the tach.