I know things... A lot of things.
Join Date: Feb 2015
Motorcycle: GSXR 750 K4
Re: L1 GSXR 750 Gear idicator not working gauges says check
If I understand correctly and the cluster shows 'CHEC' while the engine is startable and runs fine, then that would indicate a communication problem between the ECU and the dash. There's a wire running from the dash to the ECU, that's supposed to transmit serial data. On the K6/7, which is the only model for which I have a manual right now, it's the B/G wire and it should be the same on the L1, but if not, you should be able to figure out what it is, and what exact pin on the ECU connector it goes to, from the diagrams in the service manual. From your account of the problem, I suspect creeping corrosion causing communication trouble. Have you removed a pin from the ECU connector, in order to disable the EXCVA and left the hole unplugged?