TOPIC:

What is the best type of oil to use ob these vintage bikes. I have heard many stories. Is it safe to use synthetic r should I stick with regular ? also the best weight.,, thanks

Full synthetic works fine, but it MUST be motorcycle oil - not car oil. I have been using Mobil-1 Racing 4T for a number of years and it works great. Do Not use regular Mobil-1 car oil in the bike.

Here's the important information - whether you decide you use synthetic oil or standard oil it is very important that the oil you use in the bike has "JASO-MA" printed on the label. This will ensure that the oil chemistry will not damage the wet clutch in your KZ. There are numerous oils that meet this standard including some diesel oils. Most regular car oils have friction modifiers in them to improve gas mileage, and these will damage the clutch and make it slip.

Unless you live in an extremely hot climate or race the bike at the track you can use 10w-40 oil with no problem. I would not use 20W-40 or 20W-50 oil if there was a chance I would be starting the engine when the air temperature might be below 40-50* since higher viscosity oil doesn't flow as freely as lower viscosity oil when cold. The risk is that there could be insufficient lubrication when the engine is cold.
Ed

I got a gallon of 15-40 Rotella T oil from K-Mart a couple-three weeks ago for $16.00 and I saw it was on sale even $2.00 cheaper at the local Auto Zone stores here in Denver.
It says JASO-MA on the back.

Syn or dino oil works fine as long as it is rated for motorcycle service. In the USA, about 98% of the oil sold as "full synthetic" is dino oil which has been subjected to a refining process called hydrocracking which removes some more impurities. "Full syn" may also be a blend of dino base and man made.