I HAVE 1979 KAWASAKI KZ650 THAT ONE DAY WHILE RIDING STARTED LEAKING OIL FROM UNDERNEATH THE ENGINE.. I GOT OFF AND SHUTDOWN ,I HEARD NO STANGE SOUNDS PRIOR TO AND THE WHOLE CRANK CASE LEAKED OUT WITHIN 3MINS HAVE NOT LOOKED AT YET, ANY SUGESTIONS?

Sounds like big end bearing gone and oil would probably be coming from gear box and engine seam and falling on exhaust its sounds like a pretty stuffed motor but everything is fixable depending on how much coin it coast and if its worth it cya Neil

if it ran out off oil you could have seized the motor or broke the con rod

http://www.jarlef.no/Kawasaki/PDF/Z650/Files/KZ650-1981manual.pdf

The timing is sett wrong,

Friend, There could be two reasons for this. One. There is no current reaching the spark plug and thus there is no spark in the cylinder. Please remove the plug and connect again tot he HT wire. touch it to the body (metal portion) and turn the engine. If there is spark, it will show as blue flame between the points of the plug. Two. There is no gas reaching the cylinder. Ensure that it does reach there.

Check the rectifier unit? Check how much power is being charged in to the battery it should be between 12/14 amps.

If it is, as you say, a 1979 or so engine, the crankcase breather could have well worn out. This will cause the oil burning and blowby. Replace the breather as an assembly, they are cheap and available from any Briggs dealer. The leaks are probably loose bolts and/or bad gaskets. You will just have to figure where the leaks are and replace the appropriate gasket. The breather could also cause the leaks so do the breather first then run it for a while to see if it is still leaking

not sure if this will help, but the crank case has a breather tube that is around that area. if the bike is on its side or has been doing wheelies, some oil can get thru the breather hose causing that problem.