Help with Photo Tach

[mstailey]

New to using a photo tach and I can't get a steady reading. I've put 1 strip of tape across the side of the crank balancer and have been holding the photo tach steady and pretty much even with the tape. Distance from the unit to the balancer is about 8 inches. What am I doing wrong? Should the reflective tape go on the front of the balancer? Should there be more that 1 piece of tape? I've read the instructions and all it says is to add 1/4 piece of tape where needed. Called ExTech helpdesk twice - forced to leave an email with no return call. Model is Extech RPM10

Attached is how I currently have the reflective tape installed.

Thanks.

 

[Jackman]

Phototachs are so accuracte and sensative you can generally see even the smallest imperfection in the way the engine fires, which causes very slight fluctuations in rpm readings. The Tach should have a point at which it stops taking readings and displays a value. That's generally what value I use when I'm concerned with taking rpm readings. At higher rpms as opposed to idle sometimes the readings are better, less jumpy because the things that often cause rpm fluctuations are masked. I would also use the smallest piece of tape aloowed by your particular tach.

 

[Traveler 45C]

The phototach is looking for the laser being reflected back to it and it is possible that it is getting back more that one reflection.

I put the tape on the front of my crack pulleys and had no problems. But if I did, I would blacken them somehow so that only one reflection is returned.

 

[mstailey]

Thank you gents. I will try the suggestions.