Topic: Results of Spark Advancer test

[cb650guy]

Hello,
I followed the shop manual's instructions for performing the spark advancer test for my 1980 CB650 Custom.  I am puzzled by the results.

I attached the timing light to the #4 high tension cord as instructed and kept the engnie rpm above 2750.

With the timing light pointed away from the pulser generator obviously the spark advancer was spinning crazy fast.  When I shined the timing light on the spark advancer it was frozen in place at the correct timing mark.  The problem is that every once in a while (perhaps every 5 or 10 seconds) the spark advancer would flip flop.  By flip flop I mean it would very quickly (like the blink of an eye) move to a different position and then immediately come back to the correct position.  Does this mean it is not operating properly?


Hope this is clear.

Adam

[MCRider]

Hello,
I followed the shop manual's instructions for performing the spark advancer test for my 1980 CB650 Custom.  I am puzzled by the results.

I attached the timing light to the #4 high tension cord as instructed and kept the engnie rpm above 2750.

With the timing light pointed away from the pulser generator obviously the spark advancer was spinning crazy fast.  When I shined the timing light on the spark advancer it was frozen in place at the correct timing mark.  The problem is that every once in a while (perhaps every 5 or 10 seconds) the spark advancer would flip flop.  By flip flop I mean it would very quickly (like the blink of an eye) move to a different position and then immediately come back to the correct position.  Does this mean it is not operating properly?


Hope this is clear.

Adam

The "frozen in place" look is the proper look. Any deviation is either your light isn't strobing consistently or the advancer is burping. I vote for the latter. Using another light would be nice to check.

Hasten to add I'm not a 650 guy, but if it were a CB750K2, that's what I'd say. 

[cb650guy]

If the advancer is burping what does this mean I must do?  Do I need to replace it?  What problems would this cause?

Thanks,
Adam

[MCRider]

If the advancer is burping what does this mean I must do?  Do I need to replace it?  What problems would this cause?

Thanks,
Adam

Again, from the perspective of an older CB750, if it accelerates smoothly to redline in each gear, I wouldn't worry about it. Hold the throttle at various RPM levels and see if the burping is worse.  I think it would manifest itself as a "surge" at cruising speed. Or you may not feel anything at all, especially if its happening at higher RPMs where you don't cruise.

If it is a noticable surge or miss, you may have to replace it.

Hoping for others input as well, to learn.

[Gordon]

Probably just the inductive pick-up of the timing light not getting a consistent pulse from the plug wire.  It's been like that on all engines I've timed with a strobe.  Could be just because I've always used a cheap strobe light, I don't know.  The mechanical advance can't move out and back in that quickly, though.  

[MCRider]

Probably just the inductive pick-up of the timing light not getting a consistent pulse from the plug wire.  It's been like that on all engines I've timed with a strobe.  Could be just because I've always used a cheap strobe light, I don't know.  The mechanical advance can't move out and back in that quickly, though.  

That sounds good, probably the light.

When I've seen a bad advance, it is a slower, clumsier, flicker on the light. Fairly constant too.

[Hush]

Remove the advance mechanism (after marking the timing mark on the case with a felt tip pen) and give it a clean, also check the springs for a good return.
While you have it out and apart it would pay to lightly grease the posts that the weights pivot from.
It's not rocket science, I know cos I did it.

[cb650guy]

I'll give that a try also Hush.

Thanks for all of the responses guys and gals.