OK so I've been a fan of the optical sensor especially for applications like Gas engines or Non Super Tiger. The optical does need to be rewired see below.
And this works where you can get good light as in the old bird.
So this weekend I tried to install one in my RV-4. Rainy weekend so I was working in the driveway between rain drops. Try as I might it wouldn't work. I finally found that the cowl was not letting enough light in for the optical sensor to work.
This meant I needed to get creative and use the Hall effect sensor. I used my test bed back plate from an old spinner (I use it to test the optical) I drilled two holes opposite each other and cut off the excess. Then I used the balancer seen here to grind each until they were equal in weight.
Here one side has been cut.
You'll need to go to the RPM section and bump the ratio from 1:1 to 1:1.99
I'll post a picture of that working as soon as I find it.
KKKKFL