I assume that you mean the hard fibre washer between the jet block and the big base nut ? If so, be very careful that the inside diameter is well clear of the suction hole in the base of the jet block. While you are at it, push some fuse wire through all the fine drillings in the jet block to make sure that they are clear, and blow through the main jet. With modern so-called petrol the main jet needs to be at least a 190 or 200.
You are not alone in your starting problem. A friend has just finished rebuilding his Scott racer from about 30 years ago. Good compression, good suction, good spark, timing checked and rechecked. Will it start ? Will it hell ! He is mystified, but is truly a Scott expert. Years ago you could walk into a chemist’s shop and buy little bottles of anaesthetic ether. I used to use it to make model diesel engine fuel. Add a bottle of that to a tank of petrol, and poor starters would become one kick bikes ! The Elf an Safety brigade have put a stop to that…
