Hi, running an AAZ with AAZ alternator setup (been in the van 2 years now, the engine has done 100,000 miles and no pully wheel has fallen off yet

) i have lived so far with the tacho reading 1000rpm off at 60mph (act reads 4000rpm @ 60mph) i believe that you can adjust the tacho by a screw on the rear of the unit? I have looked at mine (on a 1990 Westy) but only see two brass screws,on at the top and one at the bottom, i cannot see any adjustment screw. Any ideas?
Ta.
1984 Marsala Red Pop Top Westy.