Re: problem with tiny tach on 30 Nissan 4stroke
The settings are to set the frequency divider for number of sparks per revolution of the crank. In other words, once every 2 revs -- such as for a 4-stroke car (720), once for every rev -- such as for a normal 2-stroke OB, or twice every rev as on some multicylinder motors that have distributors.
I think you will find that you are getting interference from the fairly high energy ignition, and need to locate/isolate the inductive wire differently for it to stabilize. In other words, the tach may be a bit too sensitive.
If you have the fuel-injected 30, you can monitor real-time data from the ECU, which would rule out all questions. To do so, you need a diagnostic kit 3AC729200M $325.00, available from any dealer, and also a laptop PC to run the software and collect the data from the motor. BTW, idle should be 850 (+/-30) RPM, and is not adjustable. WOT should be 5750 (+/-500) RPM, preferrably on the higher side for maximum performance, and will be determined by prop pitch, boat loading, etc...
As an alternative to the tinkertoy tach, a Factory tach is available, quite pricey -- but very reliable and dead-nuts accurate -- either with or without warning lamp. Part number 3N8-72640-1 (with lamp, configured for EP models), 3B7-72530-2 (without lamp, configured for MF and EF models). If ordering a Factory tach, consider ordering the appropriate interfacing cable as well: 3R0-72537-1 is the one that connects to the RC box leads (with warning lamp), and 361-72539-0 is the one that connects directly to the MF/EF motor (for use without warning lamp).
