Hello Nielst, and welcome to NSR-WORLD.

The 88-96 (MC18~MC28) engine mounts are rubber, so check those for wear, but there is a "torque link" between the engine and frame pivot on the MC28 (and MC18-1 & MC21).

Please see here:

http://nsr250.net/forums/members/nsr250r_manual_mc28/index.php#p=192

These can wear over time, and allow the engine to move under braking and acceleration.
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Andy.
NSR-WORLD.COM

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