Author Topic: CB500K1: electrical gremlin  (Read 474 times)

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Offline AndyH

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CB500K1: electrical gremlin
« on: April 28, 2019, 03:01:34 am »
Have just completed a fabulous 850km (530 mile) return trip from Perth to the SW of Western Australia to celebrate 50 years of the CB750.  My mate was riding my 500 (I was riding his 750K1) and it had no trouble keeping pace with the 22 750s....until late yesterday.


Roland (my mate) reported that it had instantaneously dropped to 2 cylinders for about 3 or 4 km and then straight back to 4.

When we arrived at our stay for the night we did some initial troubleshooting.  We were able to determine that cyl 1 and 4 went missing.
After removing the tank, we checked the connections to the coil in question but nothing was found.


Anyway, on the way home today it intermittently dropped 1 and 4 again and progressively got worse.  Roland managed to limp it home on variously 2 and 4 cyls.  No fluttering/fluffing, just straight to 2, then straight back to 4.

Tomorrow we plan to do more thorough troubleshooting to hopefully identify the problem.  The initial plan is to double check ALL connections and possible intermittent wire-shorts from the Dyna-S to the coils.  If that doesn't reveal anything, then we'll swap the coils over and see what that reveals.  If nothing again, then we may have to suspect the Dyna-S, which BTW has been running without issue since I 1st bought the bike, until this w/end.


For those with experience, does this sound like a good approach?  Are there any other things that we may need to look at?


Fuel issues have been ruled out.  (Someone recently remarked that 99% of fuel problems are electrical!  ;) )


Cheers
Andy


« Last Edit: April 28, 2019, 03:04:18 am by AndyH »
1972 CB500 Four K1 (AUS version) 8)
Previously owned..
1967 Honda Sports 90
1971 Yamaha CT2 175
1973 Yamaha RD250
1975 Kawasaki KX125
1983 Yamaha XT250T
BMW R65
BMW R80
BMW R100LT

Offline HondaMan

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Re: CB500K1: electrical gremlin
« Reply #1 on: April 28, 2019, 09:12:57 am »
The 500 has a history of burning out the OEM coils at around 30,000 miles of use.
But, the Dyna S has a MUCH worse lifetime than that.... :(
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Offline calj737

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Re: CB500K1: electrical gremlin
« Reply #2 on: April 28, 2019, 09:18:24 am »
Intermittent failure with a Dyna S tends to be an End of Life indication. There had been a bad "batch" of them about a year ago, but earlier units seemed more reliable.

Some have found by removing the points cover (weather appropriate) helps keep them cooler and alive longer. Worth a check.
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Offline AndyH

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Re: CB500K1: electrical gremlin
« Reply #3 on: April 30, 2019, 02:29:36 am »
We checked out the wiring today and found that the black/white male bullet in the double-female connector to the 1-4 coil appeared somewhat loose. 

We fired up the bike on the test fuel tank and I felt that the connector was getting a little warm!  Out with the emery to polish up both male bullets, and a pair of long-nose pliers to squeeze up the female side. 

Connected everything up again, and no noticeable warmth from the connector.  Rode home with all 4 pots firing as per normal.

Some longer rides are planned (weather permitting) to see if the issue returns, but I'm confident that we've identified the problem.
1972 CB500 Four K1 (AUS version) 8)
Previously owned..
1967 Honda Sports 90
1971 Yamaha CT2 175
1973 Yamaha RD250
1975 Kawasaki KX125
1983 Yamaha XT250T
BMW R65
BMW R80
BMW R100LT