Bike has been running as usual for the past 2 weeks.

Today it started fine both morning and after work. Rode 8 miles then stopped to fill up. It wouldn't start. Drained the battery a bit trying, no dice. Bump start didn't work, but a boost from a car DID, and got my the 3 miles home. When we boosted it, it went straight onto usual tickover, no lumpiness. I whacked on the lights and indicators to see if it was classic reg/reg symptoms, but it stayed alive. Put the multimeter on it when I got home:

No lights: 12.56V
All lights: 12.05

It wouldn't start up again. The spark sounded strong and those voltages are to be expected considering how much I tried to start it parked up at Sainsbury's! A month ago (last time I checked them all) the voltages were good (around 14.4V @ 5000 revs) and the resistances were perfect on the reg/rec connectors.

So I'm a little curious as to what this is about!

Dave,

Yer battery is tatties. Open and onload voltages are rubbish, 14.4v at 5k only proves the charging system is good. Get yerself a new YTX9-BS and all will be well again!

Malc wrote:Dave,

Yer battery is tatties. Open and onload voltages are rubbish, 14.4v at 5k only proves the charging system is good. Get yerself a new YTX9-BS and all will be well again!

I would go with what Malc says too. Have you had a faulty reg/rec with this battery, or have you had the battery a while?

skinnydog0_0 wrote:I would go with what Malc says too. Have you had a faulty reg/rec with this battery, or have you had the battery a while?

I think I did for about 2 months. Reg/rec went kaput last September, when I replaced that and the genny. Since then I've checked the battery and reg/rec monthly and it's always been good. There may be something up with an ignition coil or spark plug. It's not a total disaster as I need to strip it down and do valve clearances and sync the carbs. I'll just be doing it earlier than expected.

Are battery voltages with engine running? What battery voltage do you get when the engine is cranking at start-up?

Take the battery out and get it load tested?

magg wrote:Are battery voltages with engine running? What battery voltage do you get when the engine is cranking at start-up?

No, the engine wouldn't start by itself, only with jump cables.

I reckon it's the battery, is the main fuse okay?

skinnydog0_0 wrote:I reckon it's the battery, is the main fuse okay?

Main fuse is good, as are all others.

Interestingly though, my fusebox doesn't correlate with the Haynes manual.
Left to right, the Haynes manual reads (in amps): 10, 10, 20, 10.
But mine says it should be 10, 15, 10, 15 (which is what is fitted). Curious!

What does battery voltage measure when you press the starter button.