Transmission, sprockets.

Before you make any purchases you need to count the teeth on the sprockets to determine what you already have and also the condition as it may be that  you can rectify wear and sort the ratio with just one change. A smaller engine sprocket is the easy way  but will slightly increase the kickstart effort. ECGR ,  Engine ,clutch, gearbox,rear wheel ??.  You may also need a good puller for the engine sprocket.,and shorten the primary chain or fit a half link.

The book figures were Engine= 19, clutch= 42, gearbox=19, rear wheel=43.

Jonathan, My1963 88SS had a twenty tooth engine sprocket from new.  The others were as David quoted. If your bike is after 1961 it will probably have the 3/8 inch rear chain if you have to replace the gearbox or rear wheel final drive sprockets.  Good luck, Howard

Long ago (in another century!)I used a std 88 for many years as daily transport  and  went all over the country . It was usually the fastest thing I met  on the road and was cruised at up to 80 mph on half throttle with an indicated top speed of around 100 mph.  It liked to rev to 7000 rpm .  It was very reliable. Not all 88's performed this well. I suspect your bike is down on performance and with some carefull work you may find the gearing is correct.