Hi Guys,

I recently bought a 1988 NSR250 MC18 imported from Japan.
Its a bit rough around the edges but i managed to get it running with some new plugs.
After a few rides, it got really difficult to start, although im confident it has good spark and a clean fuel supply.
I've taken the decision to rebuild the engine and try and optimise its performance

Ive got a few questions.

1. The engine number is marked MC16, however, when i dropped the engine out of the frame it 'looks' like it was original and unremoved until now. Can an MC18 have an MC16 engine number?
2. I want to remove any possible air leaks (it would run lean and rpm would increase when the engine got hot). Do you know where i can source the large crankshaft seal? Would an MC21 seal fit the MC18 engine?
3. I've got a complete engine gasket kit coming, do i need to apply silicone sealant in addition to these? Im not sure if its necessary if the engine is to be stripped more frequently.
4. Do the pistons and rings need to be 'sized' or is there just one specific size? The pistons look mint, i just want to replace the rings while its torn down.
5. What mild tuning is possible while the engine is stripped? I am looking to produce 65 HP in unrestriced form but with street drivability.
6. I'm not experienced with carbs and would like to send them to a specialist here in Melbourne, Australia. Any recommendations?

I would appreciate help on any of the questions above, im glad to have a bunch of very knowledgable gurus on this forum!

Regards

Dilan