Carb' overhaul advice

[Mark]

Hi all,

I am having my girlfriends 1991 xt600E engine overhauled after 80 000 miles of use, and want to overhaul the carb's too.

I have stripped and cleaned them, and have noticed that if I push the slide up on the larger, CV carb, it stays up, instead of coming back down !
I have cleaned and lightly oiled (with WD40) the slide and the carb body where the slide fits but still it stays up. I have examined the diaphram and it has no holes, but it might be stiffer than expected.
(I have also discovered that if I block the slot above the main air passage and suck or blow on a hose coming from the top of the diaphram chamber, I can make the slide rise and fall.)

Any thoughts on the sticking slide anyone?

Also, I am planning on changing the float valve. Is there anything else I should change after so many miles?
I can't see a step in either of the needles to suggest that they are worn.
What is the method to change the needle valves, how easy is it to do?

Thanks

Mark