I've just been given a 1989 CBR 250R and it needs a bit work to be road ready so I'm apologIsing in advance to everybody if I get annoying with lots of questions but never had a roadbike before so please bare with me and bbe nice
I guess the bike you have is the wild 4 cylinder CBR250R made in the mid '80s to the mid '90s. It ran to 19,000 RPM, and was good for 180 to 200 km/hr. It was made mainly for the Japanese market, but some found their way to other countries. It is probably a fairly rare beast these days.
This forum focuses on the mild single cylinder CBR250R that first appeared on the Thai market at the end of 2010, and has been released in many other countries since then. It is quite a different machine, red lined at 10,500 RPM, and has a top speed of about 150 km/hr.
A few members of the forum have been messing around with motorcycles for years, and do quite a bit of their own maintenance. They may be able to give you some advice.
However many are new to motorcycling, and consider adjusting the drive chain an achievement.
I wish you all the best in your project, but I think you are on the wrong forum for much in the way of useful information for it.
Yeah they were sold here new for a decade or so and have been imported s/h as well so are very common, most have had a horrible life.
Apart from tuning 4 carbys they have survived like all bulletproof Hondas.
Maybe try the CBRRRRRRRRRRRRR250RRRRRRRRRRRRRRR forums, they know it backwards.
There is a forum dedicated to the old 4-cyl CBR250s. Very similar domain name to this one. But I don't recommend actually going there to ask a question unless your the type who also enjoys smashing your own nuts with a hot toaster.