daver said:I was told that they should be checked/changed every 5,000kms or 3000-3500 miles in your case.
I say check but by the time you get it all apart to look at them, you might as well replace them. Pretty cheap maintenance that saves you big before something bad happens.
check out this post:
http://www.ty4stroke.com/viewtopic.php?t=52520&highlight=