F3 was a production race class for 250 two stroke 400cc four stroke road bikes in Japan that ran until the early 90's.

Like all production series, the bikes had to be homologated, but the production numbers required for F3 were very low (in the hundreds I think).

All the manufacturers took this series very seriously indeed, made entire dedicated race bikes for it with little expense spared and fielded full factory teams with top riders.
1992 Suzuka 4 hour race.
The earlier F3 bikes (mc16 /mc18) used a large number of RS parts.
But an F3 mc21 shares virtually nothing with either a road going mc21 or an RS250;

There are specific F3 frame, forks, engine cases, crank, barrels, loom, ignition (F3 PGMII), brakes, carbs and a whole host of other parts.
This is the only complete one I know of in the UK.
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