If it's standard (or even if it's not) start by cleaning everything, checking everything.

These bikes are really easy to work on, by far the easiest of all the last generation 250's. With (or without) your workshop friend;
Get the fuel tank off (two bolts, a fuel pipe, turn the fuel tap off!)
Get the airbox lid off (6? screws), fit a new airfilter if it's filthy.
Get the airbox off (two screw clips at the base).
Get the carbs off (two screw clips at the base, make a note of where the wires, cables and pipes go)
Get the bottoms off the carbs, get the jets out, CAREFULLY make sure they're clear.
Clean it all up, put it back togeather.

Now get the inspection panel off (right hand side "middle" fairing panel) and check the RC valve timing (details here, bottom of the page).

Put it back togeather make sure you've got clean fresh fuel, new plugs and then take it for a decent run.

If your happy you've done that lot and it's still not right let us know.

I know this sounds like a lot of work, but it's not, I destroyed my NSR within hours of getting it and spent £1300 having it fixed, an absolutely stupid move (read the saga here), an incident like this now would do no more than make me text Andy as it's so annoying it's funny and then reach for the spanners.
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Please do not PM me technical questions, if you can't find it on the Forum start a thread