Michael,
Be careful when refitting the timing cover - the studs/through bolts clamp several components, i.e. the primary chaincase, the crankcase halves, the timing gear outrigger plate and the timing cover. Make sure that you retighten them in the correct order - with all other nuts loose, tighten from the LH side to clamp the crankcase halves and chaincase, then tighten the nuts that hold the outrigger plate, then finally fit and tighten the timing cover. Any other sequence will leave the internals loose whilst from the outside all bolts appear to be tight. Before fitting the timing cover, put it in place without gaskets and check for gaps between it and the crankcase and between it and the inlet ports on the barrels - then shim up accordingly before final assembly with gaskets. The use of shims and thin gaskets is preferable to thick gaskets as tightening on thick gaskets can result in distorted and eventually cracked timing covers - a common problem on S6's.
Going back to the carburettor - shortening the needle may not give you the correct mixture - not only is the needle shorter on the vertically mounted carb but the jet assembly is also shorter, thus requiring the taper to start higher up the needle. Also the fuel level is extra critical with this setup - especially as any flooding dumps neat petrol straight on to the hot exhaust pipe!
Regards,
Eddie.
