C70 / C90 Specification and Rules

C70 / C90 Specification and Rules.



Genuine Honda C70/C90. Any model, model numbers as Honda GB and Haynes manual.



Standard gearing as Haynes manual. 3 Speed only.


Head and Cylinder.

Head must be genuine Honda C70 / C90 standard parts (no patent parts).

Cylinder can be a patent part but must be standard. (i.e.: bore, stroke, inlet and outlet)

6 Volt or12 Volt allowed.

Bore and stroke as Haynes manual. 1.00mm maximum overbore allowed.



Genuine Honda standard part to Haynes manual tolerances.

No racing or performance camshafts allowed.



Standard size valves, patent parts can be used, no oversize valves or multiple cutting to valve seats allowed.



Standard parts only, patent parts can be used, sizes as Haynes manual maximum oversize 1.00mm

No racing or performance pistons allowed.


Inlet / outlet ports

Must remain standard size, no porting allowed, polishing allowed but cast marks must be visible.


Inlet manifold

Optional but bore must be standard for each class

Heat shield optional.



Optional but must point downwards.


Ignition system

Points or CDI allowed and can be genuine or standard patent parts, no electronic, performance enhancing or racing systems allowed.

CDI unit’s 12000-rpm maximum.

Standard flywheels only.

Woodruff keys must be standard (not cut, filed or stepped) and must be fitted.

Ignition timing must be set as Haynes manual and can only be adjusted to suit cam bearing wear on points models.

Coil / condenser to be standard genuine or patent part 6volt or 12 volt

Charging system optional need not be fitted.

Battery need not be fitted.

No battery ignition allowed on 70cc.


Air filter


Oil type



Oil additives



Final drive pinion




Optional, need not be fitted, this includes shaft and gear.


Spark plug

Optional, racing plugs allowed



4 Star fuels leaded or unleaded, from petrol station.

No fuel additives allowed.



Genuine Keihin carburettor only, no pattern or copy’s allowed. Must be for genuine Honda C70 / C90.

Downdraft carburettors allowed on C70 models

Float height optional

Needle and position optional

Jets optional

Choke mechanism need not be fitted.

Bore of carburettor must be to Haynes manual



Outer casings and covers can be non-genuine parts; these are cosmetic only and must not enhance performance in any way.

No oil coolers allowed

No performance enhancing parts to be used


All internal engine parts and gaskets may be genuine Honda or standard patent parts, to tolerances as stated in the Haynes manual (unless stated above).

They must be for genuine Honda C70 / C90 models.

No parts for pit bikes, monkey bikes, Chinese imports or any other copy allowed.

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