maintaining a 4-stroke

Maintaining a four stroke is not harder but it is more expensive. You have to keep up with the preventive maintenance since a failure can be very costly. If you are concerned about cost of maintenance, consider a 250cc two stroke or a more trail oriented four stroke like an XR, TTR, DRZ, etc.

It may not be "harder" to work on a 4 stroke MX'er, but they are basically little Formula 1 motors - much more complicated and expensive than a 2 stroke MX'er.

If you want to learn what 4 strokes are like to work on, look at these posts from master motor builder Eric Gorr (especially the 2nd one):

http://dirtrider.net/forums3/showthread.php?t=115200

http://www.dirtrider.net/forums3/showthread.php?t=115201

Also, look at the pic and text from Masterphil in the 4th post down on this page.

http://www.dirtrider.net/forums3/showthread.php?t=125470

On that same page, look at Masterphil's comments on the study of costs of 2 stroke vs. 4 stroke maintenance on the last post on page 1.

Rob