Starting problems could also be a faulty crank seal. My MC21 crank seal had gone, when I got the engine running it was very poor / bogging down at low RPM in first gear. Search on the discussion forum for crankcase pressure testing.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30