A clear reason?
Direct from MNZ website
24.2.4 Engines must be derived from non-competition motorcycles. Motocross, Road Racing,
Enduro and Go Kart motors and transmission parts are not permitted. There shall be
no restriction on the make, type or design of carburettor, ignition, exhaust, piston,
cam, valve springs or cooling system except for class eligibility. All engines must be
normally aspirated except F4 4 stroke engines of less than 100cc capacity, which may
be turbo or supercharged.
F4 2 stroke engines over 104cc are restricted to carburation equivalent to a single
24mm carburettor, F5 4 stroke engines over 53cc are restricted to carburation
equivalent to a single 20mm carburettor.
Link
http://www.mnz.co.nz/download/2010_M..._Miniature.pdf
Or
http://www.mnz.co.nz/competitionrules.aspx
Definitive I Think.
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