Re: 2003 RC51 WONT START HELP !!!
At the beginning you said your bike was an '03.
The ECU was located at the rear on the '00-'01's (or SP1's).
On the SP2's ('02-'06), Honda moved the ECU under the rider's seat alongside the battery.
However, under the rear cowl, at the rear, are four relays.
On the left, there is the Turn Signal relay and the Bank Angle Sensor relay (at the most rearward).
On the right side this is the Fuel Cutoff relay and the Cooling Fan Control relay (at the most rearward).
If the Bank Angle Sensor relay was badly damaged, then the bike may not start even if the engine was turning over quickly.
However, the relay itself can be checked by swapping it with a similar on, such as the headlight relay.
It's handy that Honda chose similar relays for various functions.
The ECU controls everything from an engine operation standpoint, although not directly at times.
The Converter Unit is the unit that sends energy to the coils and to the plugs.
It just takes it's orders from the ECU which is told when to send the command by the ignition pulse generator sensor behind the alternator cover.