Had the same thing with the 748, turned out to be a loose earth connection on the battery!

Everything else worked fine except the rev counter which fluctuated badly. I think the loose connection was causing sparking as the battery vibrated in the battery tray while the bike was running. As the Superbike tacho works of a pulse, this was probably over-riding or confusing the tacho and that's why it didn't work. I just tightened up the battery connection and it worked fine. Must have been when I fitted the connectors for the Optimate ... maybe if you removed the battery you have the same problem?

I had the same problem with my 748,the rev counter would work fine then if i stopped say for petrol then started the bike the needle would move and then not work.
I took it to the dealer and the rev counter was replaced,this did not solve the problem bacjk to the dealer and the connections checked and the sub wiring loom replaced again the rev counter failed.
At this point i give up and rode the bike for a season and took it back to the dealers for the mot and a new clutch also asked to check the problem over again,new ecu fitted and the problem solved,this was replaced foc.

For some bizarre reason a dodgy battery/dodgy battery connections have caused a similar problem on my 998.

As the battery on your bike has been flat and/or jump started, I'd check ou the batteru and its connections 1st before getting into replacing component mode.

It takes quite a bit of power to keep the bike running, i.e. Fuel pump, ECU, injectors and so on. For some reason the tachos seem to be very voltage sensitive.

If you have the lights on, switch em off, if that cures it or it "fixes itself" after running the bike at a fast tickover, 2 =3 k revs, for a while, I'd put it down to a low battery.

Ray