Bonneville starting mystery

Hi Steve, do you keep the bike on an Optimate or similar? In this colder weather any weakness in the battery is shown up very quickly. With the EFi Bonnies, if the battery is below a certain figure (not very low) then the ECU will not allow the start motor to be activated. A figure of 12.5v comes to mind. An easy way to test for battery weakness is to use jumpstart cables onto a known god battery. If you connect to a car battery DO NOT have the car engine running, just use the power in the cars battery. If the Bonny fires up first time, you know your bike battery needs charging/replacing.

Have you checked your sidestand and clutch switches? Also the start relay can play up. A fault on any of these will give the symptoms you describe. Have you got a multimeter to check the switches?

 

Hi steve, this has happened to me once since I have owned the bike, and like you I was confused as to why it wouldn`t start, not sure what it can be, I carried out a few obvious checks like you have, pushed on the spark plug caps etc checked kill switch but everything seemed okay. Haven`t had the problem since touch wood, be interesting if someone can shed some light on what the potential problem could be.

 

Hi Steve , see engine won't start ecu cut out, the relay is likely the culprit as dirt or water can get into it causing intermittent starting fault, ecu detects voltage drop because relay is shorting or dirty points won't allow full current flow.

 

Good luck mate.

 

Plus mine is always hooked up to the optimate4, mine came with the adaptor lead whereby you connect it to the battery and then you can just unplug or plug in as required without constantly having to take the seat off to hook it up to the battery, when I am using the bike I just tuck it up out of the way,does that make sense?

 

If you get yourself that multi-meter (about £15) you can check for any resistance across the starter relay which would indicate it's for the bin. I'm a numpty when it comes to electrics really but I watched a video just the other day which covered this.
The wires of the multi-meter will have some resistance (say 0.3 ohm), anymore than that going through the relay is not on.