I had a similar issue, but more like what Tom stated. My speed was all over the map and I figured it was a power delivery issue. I thought the motor was probably going bad. So I opened up the unit to find there was Hurst motor. Checked it out online. The motor I had was a 300 RPM 7.5 amp motor. They had the exact same motor and another one that was 9.5 amp and higher torque. Well, of course I had to go for the 9.5 amp version. What a difference. Speed is very stable now.
Scoutmaster runs very slow
I have a Scoutmaster and the SDS. When I plug the Scoutmaster directly into the wall and measure speed with the KAB Speed Strobe 10 numbers drift by, moving right, in about 5 seconds. KAB states 10 numbers in one minute represents .3% accuraccy, so I'm really slow. Using the VPS, turned up to 66 frequency, 10 numbers drift by in around 15 seconds, better but still very slow. The voltage number reads 84. I would appreciate any suggestions