Going to be taking delivery of a new Evo 250 in the next week. I've never had a new bike before. How do people run in new engines ? Advice about duration and style of running in would be appreciated as well as oil ratios for new engines.

The supplied Owners Manual covers the breakin procedures well. It is also available on the UK Beta website and the Betamotor factory site. Generally it is something like 8 hours, avoid excessive use of throttle over 3/4, vary the rpm, 1.5% fuel mix, check all fasteners etc.

Spencer

As above.

Not full beans and not to low in the revs. Pootle around working everything that moves. Check every nut and bolt before, during and after your first several rides.

Do you need to do anything to a new one before going out, such as sealing stuff up or modifying anything? Air box and so on...

Get it warm (important)and give it the berries for a few hard runs to get the rings to seat properly.

See here ... http://www.mototuneusa.com/break_in_secrets.htm

The website mentions its use for 4-strokes - any thoughts on this process for 2-strokes??

The fuel mix beta recommend is 1.5 % for fully synthetic that is 75ml in 5 litres I have just finished running in my 300 factory I ran 100ml in 5 litres of fuel for the running in period! That was fine you will need a new spark plug after 5 hours as it will get oiled up! And remember after 5 hours to changed the gearbox oil! Even after running in I run a fuel mix of 85ml in 5 litres just to be on the safe side! And as the other guys said check all nuts bolts chain etc and most important have fun new bike is the nuts!! ????