General Instructions. We recommend decarbonising about every 1,200 — 1,500 miles to get the best results.
Place the machine on stand. Take off the petrol tank. Remove sparking plug, exhaust pipes, carburetter and petrol pipe. Take off cylinder head: Remove cylinder nuts, when cylinder can be lifted off. To detach piston, first remove circlip in the boss of the piston : this is a spring steel ring and is removed by taking a pointed implement and prising up the end of the ring through the slot provided, then push gudgeon pin out. Before proceeding to do this, protect the cylinder opening in the crankcase with rag to prevent the circlip dropping into the crankcase.
When the cylinder head is removed, take great care not to damage the metal to metal joint. If this joint is damaged or leaking it should be ground in with valve grinding paste just as a valve is done. The joint is made on the broad face.
When tightening up the head bolts, take great care to tighten them up evenly and equally ; this applies to the cylinder nuts also. To remove the piston rings use a small narrow blade penknife, carefully put under ring at joint, work gradually all round till the ring has been lifted out of its groove and has fallen back again. This frees it. Now start again, but this time press the ring slightly sideways, so that it will catch on the edge of the groove and remain out. Then slip top ring over the top of piston and bottom ring down the skirt. Take care not to strain the rings sideways or they will be permanently distorted. Clear the carbon away from the outside and inside of the piston ; do not scratch the parts. The end of the screwdriver may be used, or a short piece of 3/16" diameter wire, which can be bent to make a scraper.
Now scrape carbon deposit from the cylinder head and the exhaust ports. Care should be taken not to score the inside of the cylinder barrel.
Scrape away any carbon adhering to the exhaust pipes where they fix on to the cylinder. If the pipes are badly carboned up it will have to be burnt out. It is advisable to remove carbon from exhaust pipes and silencers periodically as this obstructs the exit of the gases and causes overheating and loss of power.