GPZ-1100 1995. Changing oil in engine and fork. How much fork oil to use? And what oil is better to use in engine? Thank you.

If you are not VERY mechanically inclined...and have the special tools required... .please take this to a professional!! it will be less expensive in the long run.!!

It takes some special tools that only dealers have.

must take the fork out of the t-post. then open the top cover. drain remaining oil. push down top part of the fork until it reaches to the end. put oil leveling the top. pull the top part of the fork again. spring must be inside when filling it with oil.

it screws into the damper rod in the fork, spin it out with an air gun

Check your owner's manual or visit your dealer. They will not charge you for this info.

losen the triple tree clamps which hold the forks and slide the fork tubes up and retighten

270mls per leg

use a 15 weight oil and 270mls per leg

The anti-dive valves are easy to remove...
Place the bike on her center stand, and raise the front wheel with a jack under the front of the engine/exhaust.
first loose the 3-way connector on the lower fork part ( brakefluid ).
Remove the 2 screws that hold the upper part of the anti-dive system to the lower part. You'll see the plunger. When braking, that plunger should move about 2mm out. It must be possuble to push it back in place with fingerpressure. Then that part of valve is OK. All the parts of the plunger are separately available by a Kawasaki dealer.
The lower part of the ADVS is also easy. Just remove the 2 screws holding them to the fork tubes. The fork oil will drip out...
When reassemble, dont forget to bleed the brake hoses at the top of the plungers...
To remove the springs...
Loose both screws on the upper fork clamps.
Remove the rubber stops on the air valves
Bleed the air out of the fork pushing the air valves ( some have only 1 air valve, and an equilibration tube just below the upper fork clamp )
Remove both fork spring stops. Caution, hold them firmly down while unscreing, to avoid the stops jump away at the end of the thread!
On reassembly, the stops must be screwed at 2.3 DaN/m (17 lbf/ft ).
The quantity of oil is exactly 348cm³ in each fork. Must be filled without the springs. Push then the fork several times up and down to pump the new oil in all the valves. Then with the fork down, measure the hight between oil level and top of fork. That must be 379mm.

Hope this all helps...
Don't know about an air valve at the bottom of fork tubes...

It could be old oil or it could be spring tension. The easiest way to check which one is change the fork oil. If it still does not perform to your satisfaction, replace the springs. I would not expect the springs to wear out before 40,000 miles under normal usage for this bike. You should be changing the fork oil at least every two years, yearly would be better.