1 Longstroke engines are generally unresponsive to the advance and retard lever, the opposite of shortstroke engines. I believe that your engine has been altered by Roger Moss, and may be different to the norm…..
2 See what happens if you screw in the primary airscrew (gently !) onto its seating, and then undo it one and a half turns. This should sort out your slow speed running, BUT there are some very fine internal drillings in the carb, and you might have a speck of gunge in one of them. Gently pushing some appropriate diameter fuse wire thru’ the drillings may help. I can if necessary lend you a spare carburettor to try, or can have a look at your carb for you. It is best not to adjust the throttle stop to achieve a reliable tickover as this tends to make the engine snatch and jerk on a closed throttle/over-run situation.
This can be a bit tricky to get used to, as you have to keep the throttle slightly open when at a standstill so that the engine doesn’t stall. A little paint line on the twistgrip may help you until it becomes ‘second nature’. There shouldn’t be any need to use the air lever except when starting from cold.
3 Your gearbox has thixotropic grease in it, instead of oil, and this may be the root cause of your problem. Fill up the gearbox with paraffin, and then spin it over for a few minutes by turning the back wheel with the bike in gear. Then remove the oil level plug and carefully lay the bike over on its RH side. WATCH THE RADIATOR DOESN’T TAKE ANY WEIGHT ! Allow the gearbox to drain out into Management’s best turkey roasting tin, then repeat the paraffin rinse so as to get rid of the grease. Then fill up to the level plug hole with 140 grade gear oil. With the bike in second gear, NOT neutral, adjust the short external linkage between positive-stop mechanism and bellcrank arm, so that the second gear pair faces are level with one another. This should sort out your problems, assuming that there isn’t excessive play in the positive stop mechanism, and that there is no clutch drag.
4 I don’t know what your gearing is, but assuming that you have a 21T final drive sprocket, your bike should be perfectly happy cruising at 65 to 70 mph, but by experiment you will find that there is a speed at which you have to open the throttle a lot more to gain more speed. This causes a lot more induction roar to be audible, which can be a bit worrying to a new Scott owner, until you get to recognise it !
I hope that this rambling sorts things out for you, and would say “Don’t start pulling it to pieces unless convinced that it can’t be fixed by normal tweaking”.
Brian
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