Black deposits on pistons

All,
i was changing my gaskets on my top end and found the following (pictures) black deposits on my pistons. The readers of this forum are the best, so I wanted to throw the following questions out there:

1. What is it from?

2. How to remove it?

3. How do I prevent it from coming back?

4. Do you have any tricks of the trade or tips to reassembling my top end and gaskets with regard to sealing agents (when, where, and what types to use) ?

Thank you in advance to all of you!
Sincerely,
Arthur

1) Carbon.

2) Soak the pistons in carb dip overnight and then scrub gently with a stainless steel wire brush. Don't scrub the side of the pistons with the brush, only the crown.

3) You can't prevent it from forming. It's perfectly normal. Just make sure your carbs are properly tuned and not running overly rich or the carbon will build up abnormally fast.

4) No tricks. Only use OEM gaskets and follow the instructions about applying sealer in the strategic locations as noted in your factory Kawasaki service manual.

That's oil deposits. The clean ring around the piston suggest rings. The scratches on the piston too. It also looks like your valve guide seals are leaking. I suggest new rings, valve guide seals. What do the cylinders look like? Might as well look into them now, not when you foul plugs and have to do it again.
Steve-

It can happens for several reasons.

1. running rich over time, soot will build. Carbs not jetted correctly. Dirty air cleaners. To much fuel to air creates a rich mixture.

2. Oil entering the combustion chamber as mentioned by others. Rings, valve guides and cylinder wall grooving.

Does look like it was maybe rich, but a lot of carbon on the tops is normal. When I did my rebuild, I sanded the tops of the pistons to make them smooth to try to reduce carbon sticking.

You definitely need to replace valve guide seals. The oil drips down and then oxidizes after you turn it off and it builds up a gunk layer.

FYI to all,
Engine was bought from a barn find with 500 original miles on the odometer.
The engine was sitting for close to 30 years with zero use.
It still has less than 10,000 miles on it.
Not sure if this helps, just food for thought.

Valve guide seals. I bought Viton ones on eBay for around $28 plus shipping. The scuffs are carbon getting in between the piston and cylinders. You could reuse the rings but why? Give it a cross hatch hone, new rings, lap the valves after replacing the seals, make sure the cam chain followers aren't hard and cracking and depending on the motor the rollers. Put it together and ride the piss out of it. They're right, if too rich, carbon will build up. What's more important is washing out the rings. If that's allowed to happen, the rings won't seat, you'll burn oil and have to do it all over again.
Steve

The engine is a 1982 kz1000 csr M2.
All of the cam chain guides looked great, no drying or cracking.
The viton valve seat you were talking about- if I replace them, will I have to redo the clearances/shimming etc.?
Or is it an easy remove and replace?
Do you have a link to the item you were talking about?

Thank you again to all of you for you're replies.

The seals get hard with age and don't work anymore. I don't care how good they look. You lap the valves change the seals and adjust the valves as part of a smart refresh on the engine. Don't try to cheap out at this point, it will cost you in the long run. Plus it's embarrassing when people are looking at your beautiful vintage restored bike, you fire it up and smoke comes out. NICE BIKE.
You'll be glad you did.
Steve

The seller I bought from is SMW70SS. There are a lot of them. Mine cost 25.99.
Viton valve seals KZ900/1000

Swest- just ordered the new rings and seals.
Thanks for the advice.
A friend of mine was saying that the buildup of char on the Pistons could also be caused by the timing being a bit off. Do you think this is a possibility?

Being clean around the edges suggest rings. Classic. Put up pics of your build and if any questions just ask.
Steve