Bike dies as soon as it is started!

Do a compression test, you could have bent a valve.

have you tried the plug and carby setting .. i have a similar issue but cannot tune the carby correct

How is your clutch? Does it slip or drag when starting out? When you put it into 1st gear when starting out does the bike lunge forward? Hold it in first gear with the clutch in and rev the bike up. See if the bike wants to move forward with the clutch in.It sounds to me like your clutch isn't set right or getting worn out. Much easier to shift at low rpms on a clutch than high rpms. I hope this helps...

Either the shift linkage could be binding or you may need to adjust the clutch.
The other problem might be a synchronizer in the transmission going bad.

not sure bout the 4 strokes but my 250sx has got a level plug around the water pump. have a look there

Check the post you submitted yesterday. There are a couple solutions listed for this issue.

Dont open the throttle fully you will die...
If it stays on the track with now falls, NO problems , It's a KTM

Correct me if I'm wrong but the 250SX is a 2 Stroke engine with a Gas (1.98 Gals Unleaded Premium 91 octane Recommended) to Oil Mixture (using Motorex Cross Power 2T at a 40:1 - 60:1 depends on oil quality) and when KTM says to Change the transmission oil the amount called for is 0.7 liters engine oil using Motorex Top Speed 4T 15W50. These Quanities are from an 04 250SX could not find a 2000. So consult with your local KTM Dealer's Service Department and pickup a Owners Manual at the same time it would be in your best interest. Liter breakdown 0.7 liters = 0.739681 quart (US liquid) OR 0 quart (US liquid) and 1.47936 pt (US Liquid) / 0.7 liters = 1.47936 pt (US Liquid) OR 1 pt (US Liquid) and 0.958726 cups (US)