Yes, it's a no from me.  And Yamaha never used powder coating on any part of these bikes.  They used paint. 

cases are ok but some parts of the cases envelope the crankcase
heat dissipation suffers with powder coating so crankcase will run warmer(bad for HP)

jugs and heads are a no-no since these are the main cooling systems besides fuel

covers and such ok with powder, else just coat with flat black stove paint if that is your look

some engines are over cooled so not much you can harm other than HP

i.e. block your cars radiator because it looks cool?

So maybe you saw it in the other thread: Im done with the new paint :-)
Tomorrow I will start the ensembling of the engine.
I saw the other thread about the oil pump adjustment - I will check that.

To be honest: Because I had running problems, I cleaned the carburetor and forgot to mount the hose for the oil pump... Ran about 30 sec without oil and with some throttle acting.
Some weeks later i got a cut in the hose, so the engine ran for a while with too less oil...
So I think its my fault, or it increased the wear.
But to be safe I will check the oil pump too. Better safe than sorry.

--> How should i run the new engine? Is it neccecary to pre mix because of a richer oil mixture for the first kilometres? Or any other things i should note?

100/1 pre-mix on new engine
assure oil pump works

3 heat cycles 5 mins at idle/retorque head

run normally(race it if racing/cruise around if cruising)

no pre-mix after 1/2 tank or so

Thank you :-)

Unfortunately I lost the washers for the cylinder nuts...
More unfortunately it seems you cannot order these...
Does anybody could tell me the measurements for this washer plates?
Cant find it in the parts list etc.
I found some aluminium washers with 2 mm thickness online, but i dont know if this would be enough.

I swapped out the black oil pump line for a clear line on my 'clean up' as you can then physically 'see' the oil pumping up. Of course you can let the oil drip out of the pipe too to bleed but as you can buy 'clear' line, that's the way I went. When these bikes run right they are amazing, but it's crazy all the little things that can contribute to problems before even getting to the rings: leaky petcock, blocked gas tank breather, air filter, leaking intakes, broken reed valves, wrong plug, worn points, hot piston on a very cold day, leaky crank seal etc. etc.

Gosh don't use aluminium washers they will just squash out useless. Ive forgotten what bike but if dt250 or dt400 I don't think they have washers under the cylinder nuts down the holes in the fins which would be 10mm studs & deep 10mm alloy nuts. The head studs will be 8mm with normal thickness 8mm steel  washers not useless wafer thin washers like I see in our local $2 shop. Happy to be corrected if I've got the wrong bike or I'm on the wrong post.

OK I'm half wrong lol. Looking at a dt400 1975 on cmsl it shows a thick serated special washer under the deep cylinder nuts. But I think they're pressed into the cylinder hole where the stud comes through & it never comes out. I guess if one did happen to come out then at least they're available.

The cylinder washers often are stuck in the holes.  Be careful not to double them up.

images.cmsnl.com/img/products/washer-pla...20111155-01_549f.jpg  check out the pic of number 9. Not removable I think & not likely to fall out onnce in there. Just saying.