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Archive indexThe Mark I Mini-Motors were not originally equipped with decompressors but when the Mark II was introduced, a conversion kit was produced for fitting a decompressor to Mark I models. However, if you have a Mark I in original condition you may have problems starting it.
The problem is that the roller does not always have enough grip on the tyre to overcome the engine compression - especially if the tyre is damp. Adopting the following procedure should overcome the problem in nearly all cases.
First, engage the roller on the tyre and gently wheel the cycle backwards until you feel resistance from the engine compression. Now disengage the roller, mount the cycle and pedal off. Engage the roller. The crankshaft now has to make almost a complete turn before it hits compression, by which time the combined forces of flywheel inertia and the drive from the tyre will be enough to force it over TDC.
Roller slip can be aggravated by several causes. A badly worn roller will provoke slip in the wet. If the crankshaft is not perfectly parallel with the wheel axle there will be roller slip when wet, and excessive tyre wear when dry. Under-inflated tyres will also cause problems but when properly set up a Mini-Motor should give many miles of cyclemotoring without either slipping or eating tyres.
First published - February 1988