hi guys, my friend has just recently bought an 03 model dt and were both a bit confused with getting it to run properly.  the day he got it he rode 25miles home, once home he realised the boost bottle on the side of the airbox wasnt even connected. after reconnecting it i cant get it to idle well, the mixture screw is all the way in and it kind of idles but every now and again the revs build up to around 5k and stay there until you blip the throttle again.  the main jet is 240 and i now stock is 210, it has a dep pipe but is it possible for the jet to be too big? i can get it to run and idle fine with the choke on but cant do anything with it off. i recommended that he should buy 210, 220, and 230 main jets but im not sure tbh.

the main jet after 2000 changed to 240, with dep pipe id try a 250 or 260 as you said its fine with choke which tells me needs more fuel 

That has little to do with the boost bottle, either the fuel level (float height) in the carb is out or the pilot jet is blocked.

Needing choke at idle is a classic sign.

The main jet does nothing relevant to its size until the last 30% of your throttle.