OK well that’s a whole new subject, but if the bike is running ok now and the plug is a good colour then best to leave it and just play around with the sprockets.
Yes - but then you run into the problem of losing power! Basically the higher the gear the more effort the engine will have to put in so eventually if you go too high you will start to go slower again! So you have to find a compromise. 78 shold be possible if you’re not too heavy. Have you...