The serial number RJ12A-102556 indicates that your Suzuki RM250 is from the year 2002. Suzuki uses a coding system where the "RJ" prefix is associated with the 2002 model year. You can confirm this by checking the bike’s specifications and features that align with that model year.
your motor is a 1989 suzuki rm250 the 1988 rm250 motor started with j106 the 1989 rmX250 motor # started with j111
Around 80 mph.
32:1
No
Look at the vin tag on the steering head tube of the frame, it should have the year stamped on it.
a suzuki rm can achieve speeds up two 70 - 80 miles and hour
stock gearing around 72-75 mph
i have an rm 250 1990, it has 54 HP
Suzuki 163 Phlolina Yellow or later known as Aspen Yellow
24 clicks of compression
buy a service manual then take it apart....
Depends on if (and how may tmes) the cylinder has been bored.