i have an 85 k100 ... newbattery died jumped bike with car (not running) and bike starts right up....as soon as i remove the cable (positive) from bike it dies...please help

Get the battery checked out first. Charge it to see if it is just dead flat. If it wont take a charge then its down for the count.
It's not uncommon to get a dud from new and that sure sounds like what the problem is.
When you get a battery that works check the charging, you should get close to 13.8 volts across the battery with the engine running at above 2500rpm.
If you don't get 13.8 volts you will need to check futher to find why.

better get a multimeter real quick dabo.....

and try to learn a little about how to use it .....

k-bike wrote an excelent article about them try searching for "multimeter" something

playing with 'lectric stuff is compounded by the fact that you cant taste, smell, see, or feel the problems ..... if you can do any of those .....its far too late to recover any of it .
we have a saying in the electronics industry ..."let the smoke out huh ?"

and in many cases thats exactly what happens

sounds like a dud battery to me ....but there may be contributing circumstances.....

I agree. It sounds like the battery is flat and that you are not getting any charge from the charge circuit.

When an other battery is connected, you are using it to run everything. once disconnected, there is nothing to support the electronics and the bike dies.

Which is it? Well as you suggested new battery should work, so I suspect that the charge circuit has a problem or/and the battery is draining quickly (bad connection or lights are on or ?).

You will have to get one of the el cheapo multimeters and start checking.

back with the link for testing with a multimeter

http://k100rt.aforumfree.com/t725-using-a-test-meter-volts-amps-and-ohms