Topic: Mystery solved...Dyna S failure?

[quietlikeachurch]

I've just (halfway) solved the most annoying mechanical problem I've ever faced.  My '77 750F was running GREAT for about 2,000 miles, then about one month ago started randomly stumbling.  There was no rhyme or reason to it...the engine would crap out from time to time at various RPMs, hot or cold, and it even cut off at idle a few times.  Some days it would be a bear, and others it would run just fine.  After double-and-triple-checking the timing (and advance...with a quality strobe light) on my Dyna S, I moved on to the carbs, stripping and cleaning them.  Then I double-checked the coils and changed the plugs for good measure.  Yesterday the damn thing wouldn't run well at all, so as a last resort I swapped the Dyna out and put the points plate back in...and the bike now runs like a dream.  Most everyone I've talked to says electronic triggers usually don't fail intermittently, they just quit.  Has anyone had similar symptoms from their Dyna?  The 12 volts from the brake light wire checks out and the connectors aren't corroded at all.  Just curious if there could be something else before I send the unit back under warranty.

Thanks,
-Ian

[Steve F]

Even though you checked the voltage at the red wire to the Dyna-S, you may want to consider replacing that cheap little pin connector that Dyna supplies.  It doesn't look to me like something that will handle stress and vibration for very long.  Just a few minutes of loose/vibrating connection, and you build up a resistive layer on the connector that gets worse quickly until it just refuses to flow current.  I would check that first, then the connection you made to the tail light wiring then the fuse block for corosion. 

[MRieck]

Even though you checked the voltage at the red wire to the Dyna-S, you may want to consider replacing that cheap little pin connector that Dyna supplies.  It doesn't look to me like something that will handle stress and vibration for very long.  Just a few minutes of loose/vibrating connection, and you build up a resistive layer on the connector that gets worse quickly until it just refuses to flow current.  I would check that first, then the connection you made to the tail light wiring then the fuse block for corosion. 

That's a good point Steve. I spliced and soldered mine in

[jaknight]

Hey there, quietlikeachurch,

     I had irritating quirks showing up just as you have described.

     I tracked it down to my Dyna S; it was a connection that was loosening.  I reworked that connection, as others have mentioned, and I have never had a bit of trouble again.

     And that was thousands of miles ago........

     ~ ~ ~ jaknight ~ ~ ~