Topic: where'd the spark go?

[hymodyne]

This thing is driving me crazy, and I can't get it out of the F#$@ing garage.

 Today I tried to start the bike, after a week or so of neglect (trying to finish a dissertation, and my son is visiting). Because I had been having problems with spark on #'s 3&4, the first thing I did as I showed my bike to my son was pull the #4 plug wire and pop in a spare plug. I had my son push the start button so he could see the spark jumping across the gap. when he saw it, I put the plug back on the #4 plug and backed the bike out of the garage.

when I tried to start it outside, nothing. but now, its no spark on any plug. I checked for voltage across the points and had none.

I replaced the entire points/condenser plate, set the points gaps and still have nothing. the bike has its second set of coils off a '72 cb 500 installed currently, and I plan to upgrade to new coils in a week or two.

what's going on here? I thought that maybe the kill switch on the handlebar might have gone bad, since operating  lights and indicator for oil are functioning. whatr would make the plugs/ coils go dead? starter is working too...

hym

[cben750f0]

sounds like the power wire to the coils, it is doing the same things as if the had the kill switch on...you havent got a broken wire in the loom fromt the handle bars to the frame... the ones that are alway getting twisted when you turn the bars?... recheck the connection at the coils... and the connections at the frame where the points plate wire plug in... other than that i dunno...peace

[TwoTired]

Check for voltage across the open points while you turn the bars from one side to the other.  You may have an intermittant connection.

[hymodyne]

update...

found the  green ground wire connected to the coil mounting braces to be worn at the connector; fixed it.

traced the black/white wire from the coils in the harness up to the handlebars and re attached another weak connection back at the "Y" that connects to both coils turned on the ignition and had 1&4 again... (yay).  re-checked the ground for the coil for plugs 2&3, and found that that coil's wires still had no spark.  both coils get current from the same black/white wire, but the coil for 2&3 has no spark. so...,
I took that coil off and replaced it with the old one I took off. re-attached the wires to it and... still spark on 1&4 coil wires, no spark on plug wires coming from coil for wires 2&3...

what are the odds that I have two bad coils for cylinders 2&3?

they both are fed current from the black/white wire, why would one fire and the other not?

hym

[kghost]

Swap the coil power wires if still no fire then you got a wiring problem.

Just don't hook the plug wires to the plugs when you crank it. As swapping the wiring on the coils will make 1+4 into 2+3 and vise-a-versa.

[bryanj]

try checking inside that rubber boot thingy down by the rear brake light switch. Wires easily get unplugged there

[hymodyne]

it continues...

I checked the connections near the rear brake switch, and they're good. checked the wires from the points (Y &B) to the connection at the rear brake switch- no breaks. checked those wires from that connection to the connectors at the coils-no breaks. plugged the blue wire from the harness into the connector for the yellow (2&3) coil, and I had spark (faint spark)


tested for current at both points, one test wire grounded to the frame, the other connected to the threaded post for each point,
I had current showing at each connection, whether the points gap was open or closed...



final score: coil 1&4, (blue wire) operational coil 2&3, (yellow) not functioning...

hym

[hymodyne]

update...

I switched coils again, replacing the one that had been taken out, and got the bike to start, only to have it quit jsut as I sat my son on the back for his first ride...
the black/white wire that powers the two coils was delivering no current...

looks like I have to go into the bucket and see what's up.

hym