Anumber of bikes that feature in CMM are two-strokes – those humble, yet sometimes vexatious beasts that make many of us smile disproportionately to their engine’s capacity.
Unlike their four-stroke cousins, stinkwheels rely on not one, but two forms of compression, primary and secondary. The latter takes place, as normal, within the combustion chamber and above the piston crown, whereas the former occurs below the piston and inside the crankcase in around the crankshaft itself.
If this primary compression falls below a certain level the engine becomes hard to start and may also very well lose performance. An auxiliary effect can be the unwanted pressurisation of the transmission system if the leak is on that particular side. And this appeared to be the case with this month’s subject – my long-term regular rider, the Yamaha YL1.
