Suzuki RM 125cc 2003 learning curve!

I hope someone can advise on the following...It takes alot of time and effort to 'learn' a bike properly from a mechanics point of view, and any help to speed the process will be appreciated.

Just aquired a s/h (6 months old, VERY little use but owned by a muppet) 2003 RM125 for my son. so far need help on the following(I am awaiting a workshop manual so some Q's may be answered when it arrives)

1.Jetting/throttle response...it's crap!, OK at low, but mid range is spluttering and flat. Main jet is 490, idle is 40, needle is in middle clip...any suggestions on recommended jetting?, I live in the UK (US stock jetting was different)....it has stock pipe and reeds.

1(a). PV link/operation...was the 01/02 fault on the link fixed by 03?, how can I tell if I have the fault without removing the gearbox side case?, when viewed through the PV side case the link does seem a bit 'loose' on the lower end

2. Water ingress, I'm noticing alot of water in carb body after washing the bike(garden hose not power washer) carb clips all OK, no splits in boots, no water in fuel tank...anyone had this pb on the RM?

Hope you can help, happy new year to you all

OK many thanks guys, youve saved me alot of time effort in testing, and expense in maybe buying wrong jets etc...

No I am not covering the vents in the side, do you recommend this?, I am awaiting an airfilter cover (plastic bowl type) to enable me to wash the bike with the seat off and filter removed, up to now I have been leaving the seat on and the oiled filter installed, ....not ideal in terms of getting the bike clean but all I can do until the Xmas post gets back on track and my bits arrive!
Thanks for the reply.