TOPIC:

Hi
hoping for some help with an electrical issue when my bike gets hot and i stop for any reason and then try to restart it the starter motor will not turn over its as if when the fan is on it is draining the battery.
once cooled generally it will restart again although it does appear to be draining the battery and at the moment i have recharged and and have checked the voltage when not connected to the bike and it seems steady at 12.75 obviously it is not under load i am a real novice regarding electrics but any pointers greatly appreciated
many thanks
Paul

Hi Paul,

I had the same problem and it took some time to identify the cause. I changed the battery which made no difference. I also checked the voltage at the motor terminals when starting and this was OK as well. However, I was also lucky enough to have access to a current clamp that showed my starter motor was drawing far too much current than it should do. It turned out that I had a short in the starter motor windings - measurements indicated that the short was in the field (case) coil and not the armature. When it was cold and the winding resistance was low, this was not so much of a problem and the starter motor would spin more or less OK. However, when it was hot and the winding wire resistance increased, the starter motor would struggle to get the engine past compression. Again, I was lucky enough to have access to an old Z900 which uses the same starter motor so I just "borrowed" the starter from the Z900 and this immediately solved the problem. Starter motors are fairly rare but a number of companies offer a re-furbished motor on an exchange basis - I live in the UK but had to get one form the US but it all worked out OK in the end.

There is no guarantee that this is also the issue with your symptoms but might be worth checking out.

I'll ask you to post some voltage numbers to help you out.
1. Battery voltage when battery not hooked up to anything. This will be your baseline voltage.

2. Battery voltage when hooked up to the battery cables (on the bike) This will tell you if there is a draw on the battery when there shouldn't be any. If the battery voltage drops from baseline voltage then you have a draw on the battery which is draining the battery.

3. Battery voltage with just the key turned to the "on" position. We need to know how much the running circuits are pulling down the battery before initiating the starter.

4. Turn on the headlight and again measure the battery voltage. The headlight has a known draw on the circuit and by calculating we can determine the capacity of the battery.

5 Measure the battery voltage when trying to turn the engine over when the engine is cold. We can then calculate the amps required to turn the engine over when cold.

6. Same test with the engine hot. This will help determine if the starter is trying to draw more amperage when hot then when cold.

Thanks Gents at least i have something to go, as soon as i get a chance i will go through the procedures you have recommended

If you're lucky the starter motor may simply need a good servicing. Cleaning of the commutators, a good blow-out to rid it of the carbon-dust, perhaps a set of brushes and some attention to the front bearing and particularly the rear bushing (? - I think it's a bushing). If it is a bushing check it for elongated wear (Oval). I had a starter issue on a vehicle that turned out to be a badly worn bushing that allowed the armature to drag on the field-winding's. The manual gives instructions for some simple tests for the armature and field. If these check-out then you'll have to dig deeper as KB indicates.

guys
quick update discovered a snapped wire on my rectifier which i have now repaired, couple of quick checks with the multimeter and the battery is around 12.85 at rest,around 14v at idle, i let the bike warm up properly and once the fan comes on the voltage drops to about 12.5v, it is now pissing down with rain  in London so i cannot do any more tests but i plan to ride it to work tomorrow so hopefully will reveal if fault is gone