Bikes starts fine, runs fine but then battery goes flat after a while. Usual checks shows everything OK. Any thoughts?

So you've checked the battery is getting the right volts @ 5000 rpm then?

Drunkn Munky wrote:So you've checked the battery is getting the right volts @ 5000 rpm then?

Yup. I've now connected a voltmeter permantley to the bike as the voltages were fine when the bike is started in the garage but as you ride it they fall away.

So @ 5000rpm in the garage your getting 14.2v or there abouts and when you ride it @ 5000rpm the volts drop away?

Drunkn Munky wrote:So @ 5000rpm in the garage your getting 14.2v or there abouts and when you ride it @ 5000rpm the volts drop away?

Spot on. It seems as the bike warms up so the battery voltage drops.

Id say its either the reg/rec or alternator then, thats assuming the battery is in good nick

im pretty sure that if you're looking for a new reg/rec they are the same as the 96 CBR600 model ones. might save you a bit of downtime if your local honda dealer has one.

Sounds like an issue with the alernator. I had an elusive electrical issue similar to yours, couldn't find the culprit until I visually inspected the alternator (it was cooked).

If the problem is heat related you should try measuring the alternator winding resistance and open circuit output voltage while the engine is hot. The magnitude of any differences in reading between alternator phases is more important than the actual values and could point to a faulty phase.

The rect/reg is more difficult, but again while everything is hot try turning on the headlights etc and noting if the battery voltage changes. If the battery voltage increases with increasing electrical load, I would suspect the rect/reg.

The original rec/reg had a burnt out plug so I replaced it with a new unit. I then checked out the alternator and it had lost one phase, so replaced that with a new unit. Still no better so another new rec/reg and new battery. I have also tried an R6 rec/reg. I can only run with one headlight and then have to keep the revs up. If I get into traffic the bike will soon die. If I ride with only parking lights on the voltage stays at around 13.5. When the bike is cold voltage is around 14.5 with no lights on but as it warms up so the voltage drops.