VM 1000 RPM question

I have a VM1000 and the rpm is giving funny readout. I thought that if the engine overspeeds the rpm will flash, but go back to normal when engine speed is reduced below max (2700 rpm for the io360). My rpm will flash and then display a number like 119 or 121, then flickers back to normal rpm and then back to another unknown number. Any ideas what might be happening? Is there a means to change the max rpm in the vm1000?
Thanks,
Gary

What type of RPM transducer do you have? There's several different ones: Bendix mag pickup, Slick mag pickup, EI pickup, tach cable pickup. Each one has a little different failure mode. The first place I'd look is at the wiring connections to your DPU (assuming you have the older screw terminal type vs. the newer DSUB connectors) ... check for good connections at the terminals, tug gently to make sure they are tight in the sockets. Trace the wires all the way to the RPM pickup looking for any rubs/breaks/etc especially where it transits the firewall. If all that is Ok, then I'd suspect the transducer is failing.