These guys are very good. https://www.pjme.co.uk/

I fitted the tank from a CR125 several times on Mk1s and one on a Mk3. TBH you can do pretty much anything.

Most CR 250.

There should be a number on the bearing you are going to replace. 95% of bearing can be replaced using an internet bearing supplier.

The CRM250 is unusual in that it doesn't have any other marking but I believe it is because it was made for the Japanese market only.

What you have found is the VIN number.

viewtopic.php?f=20&t=5282

I don't know. Without being there it is very difficult. Carb is the area most likely to change. Replace the jets?

Clean out the carb.

Two obvious things to do - Place a filter between the petcock and the carb. Everytime you stop using the bike turn off the petcock. If the problem is only down to things you have discussed then you may have flooded the engine. Turn the petcock off and take the spark plug out. Leave it to dry out for...

If it is bogging in the way described then that is quite likely to be a carb problem. Take it off off clean it out. Check jets and also for any air leaks around the connectionsto the carb and inlet rubber. I know you have dione this but do recheck. Have you got the needle and pilot jets set to the o...

Have you taken the cover off the powervalve and watched it turn when reving the engine?

I'm sorry that I've irritated you. But they are a direct repleacement which 'in my' mind means that they are EXACTLY the same in every external measurement. I forget that those asking questions often require an large element of reassurance because they don't want to be led down the garden path by th...

'XR250R forks are a direct replacement for Mk1 forks and probably the best option with no work needed'

You are correct Christian. The headstock is shorter on the Mk1 so you have to swap posts.