I decided to go out for a ride lastnight, except it wouldn't start. Dash illuminates but not enough power for the starter motor. The bike had been stood about 10 days without use. On the last ride, it was a bit iffy starting from warm, and took a bit of cranking. The battery seemed weak then.

On went the charger and after only about 30 mins it started really well. I left it on charge overnight, and will see how it goes.

I have noticed that when the bike is running, revving the engine makes the dash and headlamps go slightly brighter. Does that indicate a weak battery or something else?

1) What is the best way to find the fault, ideally I don't want to replace batteries and regulator/rectifier if they are not faulty.

2) How long can your CBR be stood before the battery goes flat?

 

If the battery is more than about 4-5 years old, it is the most likely cause.
You can pull it and take to a parts house, most do a free load test/diagnostic.

To diagnose electrical issues, you should always start with a sound battery.
So don't skip this step. After you assure that, you can move on.

Here are some links to get the big picture and how to diagnose the rest of the system.

http://www.electrexworld.co.uk/pdfs/...P-PMG-&-RR.pdf

Charging System Diagnostics - Rectifier/Regulator Upgrade - Triumph Forum: Triumph Rat Motorcycle Forums

Technical Resources - Resources for Electrical Systems on Motorcycles and ATVs - ElectroSport

Ern

 

Sounds like the rectifier. Put a meter on the battery while its running and see if your getting 12.7 or so at idle and 14 while throttle up.

 

Great links, thank you! I will get myself a multimeter and start checking it over properly.