Motorcycle Repair: Yamaha XV700n Electrical, jumper cables, battery problem

Question
Yamaha 1985 XV700N sat over the winter with a few starts in between. When I tried to start it this spring the battery was dead. After jump-starting the cycle the lights flicker, the rpm gauge is at 9000 rpms and it's backfiring and running rough. The lights and rpm gauge fluctuate with the roughness of the idle. I checked the alternator voltage at the battery, it read 6 volts but again this fluctuated with the rough idle. When I jump-start it and leave the jumper cables on  it runs well and idles properly (With the rmp gauge reading properly. As soon as I remove the cables it starts rough idling and the rmp gauge pegs out again. Is this a dead battery problem or is there a more serious electrical problem waiting for me?

Answer
Hi David,

I suspect the charging system may be defective. I also suspect fuel in the carburetors has varnished.

Jump starting a MC from a larger battery such as a truck or car battery may harm the chrging system and MC battery.

You must use a fully charged battery in good condition when performing electrical testing or test results may be inaccurate.

Check out Electro Sport's charging system "Fault Finding Chart"....

www.electrosport.com/electrosport_fault_finding.html

Respectfully,
Mark Shively