Darn, it leaks petrol, from the carb. Nothing major, it looks for all the world simply to be a matter of a perished gasket. An investigation was in order, so the tank came off (just one bolt, after I’d removed the seat unit) and then it was a case of loosening the two nuts on the inlet manifold and the one jubilee-type clip on the airbox boot. It’s a tight fit though, so the airbox had to be loosened too, to allow the wiggle room to remove the carb. One skinned knuckle later the job was done. While doing this I’d taken the cap off the top of the carb and removed the slide and needle to find both in great condition with very little sign of wear or scoring.
The carb is a Keihin PWK22 and is a masterpiece of simplicity. One slide, one needle, one spring-clip to hold the float bowl, then simply a float and two jets, one for idle, one main jet. Oh, and one brass float bowl drain screw. This seemed to be the source of the leaking, there looking to be a fibre washer acting as the seal (or not). Of course it refused to undo. In my misplaced enthusiasm I applied bigger and bigger screwdrivers until eventually I figured a set of mole grips would be best. These snugged on nicely but then on turning simply twisted the head off the screw leaving the thread in place... A stupid act of impetuousness, I was immediately filled with remorse. It just needed some heat, or at least soaking in releasing agent and that screw would have budged easily. Dummkof! Now I’ll still need to do that, but will need a screw extractor to finish the job, hopefully without murdering the thread in the float bowl. A lesson to be learned there.
In the meantime a little online researched revealed a great trials parts specialist called Trail & Trials UK (www.tytrials.co.uk) where John Cane keeps an excellent stock of new old stock (NOS) and pattern parts for trail and trials bikes of the 70s, 80s – well, through to today. One pleasant phone call later I had a complete carb gasket kit, plus a bundle of other parts, all for little more than beer money (so very ‘trials’). John was also a good source of knowledge, among other matters warning me to be ready for when the valve stem seals give up – they perish given long periods of inactivity. You can tell they’ve gone, he said, by the plumes of smoke from the exhaust that come as a consequence. Maybe not immediately, but soon enough.