Two-stroke Know How part 1 Two-stroke guru!

We get to meet a two-stroke fan and engineer who rides the bikes he modifies.

- ROB PEMBERTON AND STEVE COOPER

Meet Rob Pemberton from SPAMotorcycles, Cheltenham, one of the nicest guys out there who just so happens to carry a torch for the humble two-stroke.

He’s also a gifted mechanic and a substantially more than capable two-stroke tuner. Thankfully he also has an enquiring and open mind which means he’s very aware that running stinkwheels in the 21st century is a challenge. You might think that you only need tech-heads if you’re planning to run a tuned bike, but that’s very often not the case. Like many others, Rob is only too painfully aware that petrol has changed dramatically in recent years and especially so since the advent of modern, unleaded fuel that contains the now mandatory ethanol.

To quote the man: “There was a time when you could rip merry hell out of the various ports then up the compression ratio of a two-stroke and it would fly. Sadly that’s not the case now and if such an approach does work then it’s more by luck than judgement. Modern pump petrol, even Supergreen high octane, bears little resemblance to even the roughest Two Star pre-1988. The fuel we buy now is designed specifically for injected engines that are purposely designed to run high compression ratios and lean burn technology in the name of low emissions. Old motorcycles in general, and two-strokes in particular, simply don’t figure on the petrol companies’ radars. Add in the introduction of ethanol to every commercial fuel pump sold across the UK and things aren’t getting any easier for those that love their strokers! The old-style fuels were effectively much slower burning than the modern petrol and this alone cause riders untold headaches when it comes to getting their bikes to run as they should.”