Background: I'm restoring a '90 K75. Project has been on hold for the past 6-7 years. Originally I took the bike apart, powder coated the frame then shot the plastic bits put it back together sufficiently to be able to roll it around. And then it sat until COVID-19 created a time when I really needed a project to keep from going bonkers. Well it's almost back together. The painting on the plastic however was marred a bit while sitting, not to mention parts being lost etc. So I decided to hit the various bits with a single rattle can, reassemble until I can see it's up and running and then get into a major paint job. I've done this before and there are several key factors I've not firmed up yet.
Phase 1: I look around the garage and have multiple cans of spray paint including one Dupli-Color Silver for a Toyota my ex used to have. Great, and there's a really large spray can of clear that advises it's good for protection against UV. Super! As mentioned some parts, tank, rear tail piece, side panels, were already painted one or more shades of silver. So Hey, it's a good day for painting. I've wet sanded the parts to be done, the temps are 80degrees F./25C and very light winds. Last few days have seen winds of 35-45 mph. So it's ho for outside and shoot the parts, front fender(2pcs) and the radiator cowling(2pcs). Silver goes on great. It's flashing as fast as it hits the parts. In fact it may be flashing just a tad too fast. By flashing I mean drying. The paint solvent evaporates i.e. flahes. Time depends on temperature and humidity. But it goes on fine and looks quite nice and shiny. So now the UV protecting clear coat. Hmm, the bright silver seems to be dulling with the addition of the clear coat. But I'm outside with sunglasses on and think it'll probably clear up as it dries. Whoa, what was a pretty shiny nice silver with addition of the clear coat is now a very good imitation military gray. Damn.!

Phase 2: So off to my friendly car/cycle paint shop, San Leandro Color. I've shot (i.e. painted) a number of bikes. You do that when the shiny side won't stay upright. But not for the past 10+ years. And when I did it I used a hardner in the paint which is now not quite legal. So I have to educate myself again. But I do have all the necessary equipment, guns, compressors, even a positive air flow system so I don't breath in anything too lethal.   I get down to the paint store and ask the friendly guy in a mask behind the counter for a graduate education in current paint systems. It seems in my case there are three:
1. seimi-traditional: using my spray gun/compressor setup buy by the tin. Shoot in color and top off with clear coat. The bottom/color coat is reduced 1:1 with reducer. The clear coat has an activator which you add to it before spraying. Cleanup is with lacquer thinner. Approx cost for smallest quantity USD $180. Probably would have half left over.
2. Rattle can Single stage with activator: This is the system used by racer boys who know they're going to be re-painting the bike after the season due to drops etc. You buy by the rattle can but with new tech. There is now a button of the bottom of the can where it used to just be curved up. Pressing the button releases activator into the paint and you have X number of minutes to shoot the target object before the paint in the can turns to rock or solidified paint. Approx $35/can.
3. Rattle can Two can/Stage with activator: Kind of old and new. You buy two rattle cans. They are separate color and clear coat. But the clear coat can has the activator button arrangement. You shoot the color, let it flash, then shoot the clear coat after activating it. Approx cost USD $80. for the set of cans. And of course you may or may not need multiples.
The store can mix up whatever color you want using standards from all the major auto/motorcycle manufacturers. So I go home to contemplate approaches.

Phase 3: I get home look at the trashed paint job parts and think ok, now for a lot of wet sanding. But hey what happens if just apply acetone? Just an experiment. There was no activator used. So 3/4 gallon of acetone, a bunch of rags and the bad paint job is essentially wiped off. Took more time and effort than I'm letting on. But then to wet sand it. And the thought hits me. I haven't really committed to a final paint scheme YET. And what if I just want to do a trial run??

Anyway, that's what I learned today the hard way. Hope the intel is of some use to others.
best regards.

Good information.  I have done paint jobs and repairs now to five bikes in the past 6 years.  I have evolved a system that works pretty well for me, making the final painting pretty painless. 

I used to paint boats with stuff like Imron and Awlgrip and 2K polyurethane clears.  The recipes for these paints are too complicated for someone who isn't shooting them on a daily basis, not to mention how dangerous they are to work with.

Since I'm not painting show bikes, and I have reached that age where an occasional drop in a parking lot is a fact of life, I don't go nuts, but still want a nice looking paint job.  The easiest system I have found is to have a paint shop mix the base and mid coat(if required) and then clear with a 2K rattle can.  The base and mid are acrylic enamels, the clear is not polyurethane, but probably an acrylic.  If needed, it wet sands and buffs out easily with nice results.  Once the hardener for the clear is activated, you have up to 5-7 days to shoot the contents if you put it in the freezer when you are done for the day.  The clear takes about 2 weeks or more to get full hardness, and isn't as hard as the polyurethane clears I used on boats, but it's a lot easieer to use.  3 medium wet coats are the minimum.

For flexible parts like front mudguards and K1100RS belly pans it's a good idea to use an adhesion promoter between the part and the primer and the primer and the base coat.

3 inch foam pads on a DA orbital buffer with 3m Perfect-It #2 and #3 after wet sanding with 2000 and 2500 will take care of any orange peel. 

You probably know that prep is the most important part of the job.  I've had pretty good results with SEM high build primer/surfacer in light gray.

A lot of newer finishes are called Tri-Coat.  Several of the K bike finishes are included such as Pearlmut Silver and Mystic red.  They consist of a metallic base coat(usually silver) a mid-coat that is a transparent color coat with a very fine reflective filler(usually mica flakes) suspended in the paint.  The effect is a very deep metallic look with soft highlights and subtle color shifts.  Think of the old candy apple red with reflective flakes in the candy.  Pearlmut has a slight gold tint that varies from different viewing angles.

These tri-coat paints are a bitch to get right.  You have to get exactly the right amount of mid-coat to get the color right.  The trouble is that you don't know what you have until the clear goes on.  They also have a tendency to show "stripes" where different amounts of mid-coat have been applied because of poor gun control.

2K refers to the fact that the clear is mixed with a catalyst to speed up the cure of the paint.  It's a term you will see used by painters to differentiate it from regular paints that do not have catalyst activators or hardeners.  It's a type of paint, not a brand.

Your comment about putting clear on the silver reminds that not all paints are designed for clear coating.  Some colors just don't work with clear.  I painted the wheels of one of my bikes with Rustoleum Silver and had the same problem when I put clear over them.  You have to read the directions on the can to see if the clear will work properly.

Thanks that clears up those points. Frankly right now it sounds rather out of my depth for what I'm doing. Which is just getting it splashed so I can take it out on the road as soon as DMV deigns to send me my tags. But I'm sure some one will be able to take advantage of the intel.
best regards

Thanks for the explanation guys, much appreciated 

Decided to try the single stage activated rattle can approach. Judging by the several admonitions and patent statements on the can this product appears to be available in Canada as well as the US.

The process is fairly similar to regular painting with a rattle can. 1.) you shake it for a minimum of 2 minutes. 2.) you take the red button which is attached to the can cover off and insert it onto the pin sticking out of the bottom of the can. If you look at most spray cans you will see the bottom is concave. The pin is situated in this cavity. You then hit the red button, i.e. pin, with a hammer. Drives the pin up into the can releasing the activator into the can. 3.) you shake the can for another 2 minutes and spray. I was told to NOT spray in direct sunlight. Wasn't told why not. So I shot the 4 pieces (2 cowlings, 2 fender pieces) in the garage door with a fan blowing out. Less fumes for me to breath. Job actually looked very good. And at this point I think a clear coat wouldn't actually add anything. The paint store folks said that one can covers about 3 square feet. Translated into my project I think I only used between 1/2-2/3. I am told that the paint has a pot life of 8 hours and takes 24-36 hours to completely set. Tried the suggestion of putting the remainder in the freezer and will see how long that will prolong the pot life.

Still waiting to see how it finishes out. But right now the pieces look very nice.

You hit the button with a hammer?!  You just need to give it a good push with the heel of your hand.

You don't paint in the sun because the surface will be too hot and will mess up the finish because it will flash off before it has a chance to let the orange peel flow out.

Even though it says the paint is hard in 36-48 hours, it will be soft enough to be messed up by anything putting a little force on it for a long period.  Real hardness takes about 2-3 weeks.

Figure it will be good for 4-5 days in the freezer.

Point-Seven-five wrote:You hit the button with a hammer?!  You just need to give it a good push with the heel of your hand.

I was just following the directions from the fellow that sold me the stuff. It worked and didn't leak or otherwise appear to have any issues.How long do you think it should warm up after being taken out of the freezer?

Just re-covered the saddle on my main bike. Saddle was one of the Corbins and the textured portion of the Vinyl had begun breaking apart. Called Corbin up about re-covering it. They wanted $400. Found a upholsterer that would do it for $150. with me supplying the material. Looks good. So I'm going to give it the old one hour test and ride around the bay.

best regards to you guys.

I run hot water over the can for a couple minutes or put it in the sun out on the driveway.  I don't use it until it just starts to feel warm in my hand.  The warmth makes sure there is lots of pressure to get good atomization.