Motorcycle Repair: CBX 1000 Z whirring after engine stall, cbx 1000, starter clutch

Question
Hi again Jan

Another concern on the recently purchased CBX 1000 Z, 1979.

In this mild weather, the choke fast idle setting may be incorrect. Too much choke is too rich, but correct choke leads to engine low RPM and stall. That's of no concern, unless the stall relates to the next problem (it simply needs adjusting, I hope).

The problem is that when the engine runs for a few seconds or more, but then stalls, as it comes to a stop, there is a whirring sound. It sounds EXACTLY like the starter motor when you release the start button after the engine fires up during a normal start - a rapid whirring, which gradually diminishes over a period of a second or two.

It's as if (in my imagination) the starter hasn't disengaged, but that it does disengage when the engine stalls. It may even be that this is causing the stalling, not the fast idle adjustment.

This may require a follow up question(s), unless you immediately know what it is from the above description.

With Thanks and Best Regards
David  

Answer
Hi David,

The starter motor on a CBX actually has a typical motorcycle starter clutch, which consists of three rollers on a smooth spindle.  The starter never actually 'disengages' but the starter clutch rotates freely in one direction and locks up in the other.  I have heard of these clutches slipping when they are supposed to lock, this happens with old oil, or if there are irregularities on the smooth surface of the spindle, caused by deformation or corrosion.  This can give a whirring sound when trying to start, not after starting. Awhirring sound after starting could be a bearing in the starter motor.  Changing the oil is easy; do that first.  The starter is also fairly easily swapped, do that next if the noise comes from there.  Any work on the the starter clutch is a very major engine overhaul procedure, and may be a reason to sell a CBX cheaper than perhaps it should have been :-(
Good luck,  Jan