8N51 Proofmeter

[Btzj02]

Has anyone purchased a proof meter recently that is accurate for an 8N51?

I have been reading the archives regarding inaccurate proof meter readings. Seems there is a difference between a NAA and an 8N proof meter. According to previous posts if the NAA proof meter is used on an 8N the RPM readings will be 1.56 times faster. That is exactly my problem. Archives also say that the face of the NAA says the time running is based on 1515 RPM. My proof meter says time is based on 1580 RPM. So it should be for 8N. BUT:

At high scale Proof meter reads 2450 RPM, clamp on Tach reads 1450 RPM and a strobe on the PTO shaft reads 516 RPM. I believe I have an NAA Tachometer that looks like an 8N tachometer. I am working with YT to address the problem but was hoping someone on the forum could help.

 

[deanostoybox]

Not recently, but about three years ago amid several complaints of them being off. Thought I might have gotten a bad one as I could not get idle below 900 RPM, but had a friend clock me running wide open on the road.He said I was going about 15 MPH best he could tell, that matched with the proofmeter reading above 14 MPH. Later I put a clutch in a 2N for a fellow and while waiting for the clutch parts to come in rebuilt his distributor and carburetor. Put the carb on my tractor to test and was able to get a very nice idle down to 350 RPM. Found the idle ports at the throttle plate on my carb had some hard lead deposits in them. After cleaning that out I now can get my engine to idle at 400. So I am convinced that the proofmeter I got was one of the good ones Still see folks complain about them not reading right from time to time. Guess it is hit or miss.

 

[Btzj02]

My temporary fix is old school. Adjusted governor so 100% throttle is 2150 RPM to keep me out of trouble. 0% throttle is 550 RPM. Marked the throttle plate for 1600 RPM for PTO.