Is there any advantage in term of stiffness in replacing the 400 springs with 600 3en?? Got a few spares with the 600 engine and got the 600 forks as I need the front end a lot stiffer...

Also can the springs and oil be changed without removing the forks as I noticed the drain screw and the bottom of the legs.

yes you can do them in the bike but it's easier to drain them with the forks off the bike.
I don't really know about the springs - I guess they'll be stiffer, 400's a sprug softly as standard, but there sould be spacers at the top of them, you can cut a longer spacer to increse their compression a bit but if they're too long the spring coils will be solid.
Migth be an idea to get some uprated springs

as evil said it's best to take the forks out
these type of forks are damper rod and so have small holes in the damper that the oil is forced through
so if you just let them drain your not going to know how much oil is left in em
ergo when you fill em back up your not going to be sure how much oil is in each leg, you can vary the amount of oil depending on how you want the front to feel
but each leg has to have the same amount of oil or you'll have all sorts of problems up front, like diving to one side under heavy breaking,
as for the springs even 600 ones will be old,
i'd go for new springs and spacers weight related rather than just progressive springs, but that's just me

ok... any preference of spring manufacture found these which seem good. http://www.moto-racing.co.uk/item--K-Te ... +Fork.html

Also is it a must to change the oil when changing spring .. can the springs be changed without the oil.

Ask http://www.k-tech.uk.com/ for some springs and yes you need new oil

cheers for the link... did try a set of 600 springs in the forks tonight, the 600 springs are longer and heavier but made very little difference.. new springs need after I've recovered from xmas....

just for some variety you could try maxton

http://www.maxtonsuspension.co.uk/

probably best to phone em up and get some advice on what you'll need
i think the phone numbers on the contact page,
very helpful when i used em

fzr400rr PDF from maxton
http://www.mediafire.com/download.php?d5vf4xsmjucr6m6

best bets probably uprated springs and spacers
you'd probably get a second hand set of modern forks off a newer bike that fit for the money they want just to convert to cartridge type forks but it depends on budget and use

The guy is from the States and has a Genesis (38mm dia forks)

oops
scrub that PDF then but if you try em they'll probably come up with something given the standard dimensions of springs and spacers, although postage might be the killer

assumption being the mother of all cock-ups,
but there is something to be said for adding a location and bike to the profile (something yam george is keen on i do believe )