When should I change timing belt?

I think Honda recommends 40,000 miles though your probably OK up to 60,000 miles. When in doubt (and for peace of mind) just replace them so you do not have to worry about bending your valves . It's easily done with out too many curse words by the home mechanic. With a 10 mm open end wrench take off the front belt covers. You can actually wiggle the bolts and the covers out with out draining and removing the radiators. Now take a 17 mm wrench and remove the valve type cap on the top left side of the engine,also remove the same cap on the back left side of the motor over the stator. Now put a 17 mm socket on a short breaker bar through the stator hole and rotate the motor until the T-1 mark is visible through the top hole. Now double check that the dots on the cam pulley's line up with the arrows on the back side of the covers still on the machine(outside edges). These are the cam timing marks. If everything lines up loosen the belt tensioner bolts and replace belts. Don't rotate the motor. Be sure and triple check that all the marks line up after tightening tensioner bolts. If all is OK reassemble in reverse order. bike should run exactly the same as it did before procedure.