'78 B2 Smoking Wires

Bought a fixer '78 B2. Bike hasnt ran since I bought it. According to the prev owner the stator was bad and couldnt charge the battery. I bought new stator and battery but couldnt get it started by the starter (wouldnt turn the motor at all) or kicking it. The solenoid opened closed very slowly/intermittently. I removed the starter and put it across a charged bat and starter is good.

I then started ohming out the the harness and found 12v between the cylinder head the (-)bat terminal. I yanked the (-) ground strap between the motor and battery and measured 15K in resistance, it was heavily corroded. I replaced the ground strap and all was good so I thought.

I reinstalled the starter and it turned the motor (it didnt start as I had the tank off/ no gas) I then saw a puff of smoke coming from the harness after several seconds. I dont know if this is from and I couldnt find the source of the smoke or any damaged wireing. no fuses blew.

I then set out to find any shorts and other than 5ohms between yel/red ignition line and ground, which is just the coil resistance I dont see anything wrong. I just kinda freaked out and dont want to start a fire, any suggestions on what else to look for?

Thanks Wayne

wayneosdias wrote:
I then started ohming out the the harness and found 12v between the cylinder head the (-)bat terminal. I yanked the (-) ground strap between the motor and battery and measured 15K in resistance, it was heavily corroded. I replaced the ground strap and all was good so I thought.

Thanks Wayne

I don't understand. The negative battery terminal should be attached to ground at the engine. The cylinder head would also be ground. How can you be reading 12V between ground and ground? Ed

650ed wrote:

wayneosdias wrote:
I then started ohming out the the harness and found 12v between the cylinder head the (-)bat terminal. I yanked the (-) ground strap between the motor and battery and measured 15K in resistance, it was heavily corroded. I replaced the ground strap and all was good so I thought.

Thanks Wayne

I don't understand. The negative battery terminal should be attached to ground at the engine. The cylinder head would also be ground. How can you be reading 12V between ground and ground? Ed

Negative bat terminal is attached to ground at the engine via a ground strap. I measured the serial resistance of the ground strap around 15k, For an 8g wire a foot long Id imagine the nominal resitance would be <0.1 ohms. Depending on what the actual load resistance vs the ground strap resistance the engine block was floating way above ground. This make sense that the starter didnt work on the bike as there was little to no potential on its poles.

If it were me, I'd get some 6 awg welding cable and replace the negative connection to the engine block. Some people might use 4 awg, but it depends on how much room you've got for the larger conductor.

I think a forum member "Wireman" mentioned using an old set of car jumper wires cut up as a good substitute. You'll still need to get the new terminals crimped/swaged on the wire ends.

Some welding supply places might be able to do this for you, if not, try the battery places.

MFolks wrote: If it were me, I'd get some 6 awg welding cable and replace the negative connection to the engine block. Some people might use 4 awg, but it depends on how much room you've got for the larger conductor.

I think a forum member "Wireman" mentioned using an old set of car jumper wires cut up as a good substitute. You'll still need to get the new terminals crimped/swaged on the wire ends.

Some welding supply places might be able to do this for you, if not, try the battery places.

Thanks M,

For diagnostics at the moment the ground strap I have in now is sufficient, seems to carry the current w/o heating, but once I button her up I need to get something heavy duty in there. As a note; initially thought that that joints between the ring terminals and wire were bad and I was gonna cut off the ends and put new ring terminals on. As I cut down the wire its conductors were completely corroded the entire length!?

Where I saw the smoke come from was in the main harness under the tank area where the wires are bunched and bundled.

I would cut the tape off of the harness in the suspected area. If the ground from batt- is to small, it will pull amps through the Black/yellow ground wire that is for the chassis electrical.

Motor Head wrote: If the ground from batt- is to small, it will pull amps through the Black/yellow ground wire that is for the chassis electrical.

Ah yes! Perfect sense.

Thanks Motor Head and MFolks!

That would only be 14 gauge and would heat way before the cable from Batt- and engine block. Do you have a 14 gauge from Batt- to frame ground?

Motor Head wrote: That would only be 14 gauge and would heat way before the cable from Batt- and engine block. Do you have a 14 gauge from Batt- to frame ground?

Frame ground being the black/vellow wire? I only replaced the battery/block strap w/a 10g which is considerably thinner that whatever the oem cable was. Where I got the 10g they had some enormous 2g for mowers, but the ring terminals were just way too big to fit the battery or the block. The more I think on it I think your right on w/your assessment about the strap being insufficient and current being forced thru the chassis ground. Granted my only knowledge w/this bike and its wiring is from the Clymers schematic that is difficult to follow.

kzrider.com/filebase/doc_download/290-z650b2-c2
Try this, its in the "File Base"
here on KZR. Upper right corner of the tool bar on this page.

Motor Head wrote: kzrider.com/filebase/doc_download/290-z650b2-c2
Try this, its in the "File Base"
here on KZR. Upper right corner of the tool bar on this page.

Excellent, much obliged kind sir!

Cheers

Corrosion inside the battery cables on cars is quits common,so I'd expect the same for motorcycle cables. I've found that if the cable feels "Crunchy" when flexed, it's time for new ones.

Most batteries go through a charge/discharge cycle when used, generating a corrosive gas that will attack nearby metal and battery cables.