Vibration or voltage....

[robint]

I know its a V twin but which V is causing my headlamp to blow after about 3-4 hours riding - its the standard Sport shell and light unit with BA20D fitting. Tried assorted bulbs - halogen 35W lasted least, 40/45W Bosch probably just the longest but not much in it really. Battery is fairly new (18 months) and holds charge fine, sitting at 12.3V at rest (and after 4 months non-use) whilst when running goes up to about 14.7V, though as the rev counter is just an indicator that the engine is running I don't know at what revs! Certainly didn't want to rev it much more as noise was high and bike was vibrating its way down the garage on its centre stand.........

The vibration is very noticeable - engine bolts are tight and carbs in balance (it idles at 1750rpm and revs to 8500 plus in 4th and 5th) but fingers tingle/go numb and odd bolts loosen and a couple of indicator stems have snapped ( in 2k miles) so something isn't quite right. Doesn't use any oil, no leaks and usually starts first (good) kick - though not at the Hartside Cafe on Tuesday for some reason. Rode 350 miles on Tuesday without a problem (apart from the obligatory bulb blowing) longest trip for a while in a day to add to the 22K miles on the clock.

So question is - which do I deal with vibes or volts (or a bit of both) and any solutions to the blowing headlamp bulb other than change the shell etc to fit H4 bulbs and rubber mount everything (how??).