Hmmm. Ok, thanks P, will look into it

if you put a multimeter on the battery terminals and rev the bike to 4k, it should show around 14 - 15 volts.
anything more, rectifiers goosed, anything less then possibly gene again, or rectifier but make sure the battery has 12v in to start with and is healthy.

I know from a recent trip to the bike shop that the battery has 12v but is only charging at 13.3v when revving anything above idle... they said that was lower than it should be but much better than the old alternator that was only 11.2v or something when revving above idle.

When you say the bike will not start, do you mean fire up or that the starter motor does not run when you press the start button?

It cranks, but will not fire up

If you are getting 13.3 volts at the battery at any revs above idle then the charging system is ok, RVF lights always on is a good test load for the charging system. If the engine cranks easy on the starter then the battery is probably ok too, although you can measure the battery voltage when you press the starter button and check that it does not drop below 10 volts.

Do your headlights come on with ignition on and do they go out when you press the starter button.

Headlights come on with ignition... When you ask do they go out when I press the button, do you mean off for good, or just a bit? I think they stay on but can't say for sure...

You've checked the fuel vacume pipe havent you em?

Not yet - my bike doesn't get the luxury of the garage since it's been booted out by a crappy car so it's under a cover in the garden, and I don't fancy the idea of searching in the cold and the wet for one of many pipes lol. But tbh Tony, it does sound like it could be that - I'm hopeful as having read up on it a bit more it certainly sounds similar to the probs I'm experiencing. I'm hoping it won't be too expensive too.

Tut tut, get your house in order........ bike in garage car on the drive