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Discussion Starter #1
I've got an older EX500 ('89, A3) that suddenly developed a tach that reads (likely) twice the actual RPMs that the motor is running. I've:

a) Checked the wiring harness - no shorts / opens, verified that CDI box to coil circuit wiring is not shorted together or to ground
b) Checked the pickup coils - in spec, no shorts / opens
c) Checked the ignition coils - in spec, no shorts / opens
d) Swapped a (used) CDI box in, no change
e) Replaced Plugs - no change
f) Swapped Coils & caps - no change
g) Replaced Coils & Caps - no change

I put a frequency counter on the output circuit for #1 cylinder, and it would suggest that the tach is "reading" correctly (i.e. 45-50 Hz for 2500-3000 RPM tach reading where I would "expect" 22.5-25Hz for 1250-1500 RPM tach readings). Can anyone verify that the tach on an A-Series EX500 gets "one" pulse per rev, or does it get two?

Any thoughts? (And no, I don't have another tach to swap out yet...)

Thanks!
 

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Discussion Starter #2
Post Mortem...

As it turns out, it WAS the tach. It also seems that I had a voltage regulator that finally hard failed in a destructive way (referencing the aforementioned 'bad' tach).

I had decided while waiting for the replacement tach to arrive that I'd take the bike out for a short ride. At the worst possible point in the ride (at a really bad/busy intersection, the bike decides to die out like it was gas starved, except the dash lights started to go dim. Battery failure? Not likely, as I had just replaced the battery two months earlier. I now wonder after the fact if the battery had failed due to the bad regulator/rectifier. It didn't test bad when the battery was replaced. But I digress.

After managing to pushstart the bike and make it home, I find that I have 7.6 VDC from the battery. Rechecked the stator - OK. Reckeched the regulator/rectifier - BAD. The battery recharged fine and holds voltage. Now all I have to do is wait for more used parts... :(
 

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Discussion Starter #3
All Fixed!

:D

It was likely the regulator/rectifier that fried the tach. After waiting on and finally installing the last of the parts, all is well. There are a few points for EX500 owners I'll share:

1) Always check and ensure that you haven't managed to 'pin' any of the gauge needles against the needle stop pins when you reasseble the dash - especially the temp gauge - so that you don't wind up thinking that your bike is cursed or punishing you, and doesn't want to ever work properly again. :oops: It also avoids having to completely disassemble the bike again to open the @$%@ dash up again just to unpin the @^$%@ needle. :lol:

2) Verify for certain that your generator/alternator windings are putting out 60VAC at 4000 RPMs so that if something else happens, you don't have to wonder if you need to start opening engine covers.

3) Always start out with a fully charged battery, so that if you have to wind up running the bike for short stretches on the battery only, you can do so long enough to get home. If you run on battery only, you can substantially increase the bike's likely run time by disconnecting the headlight, though at the cost of the safety factor of not having the light on and a possible "invitation to repair" notice from the local law enforcement folks.

Thanks for "listening"... :)
 
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