Use the timing disc provided in the Kent kit. DONT USE THE TIMING MARKS!

Find TDC, fit the disk to the pulley bolt, and attach a wire to the rollbar as a marker. Rotate the crank to the degrees listed for your cam (118 degrees BTDC but check to make sure)

At this point No1 cylinder inlet valve should be fully open (I'm going from memory here so please check the Kent instructions). You can measure this using a tappet in the bore. I must stress at this point, that during this procedure, no rocker arms are installed!
Having determined this point, slip on the belt, and using the vernier pulley adjust back to the desired position before nipping up the bolts. You can now install the rocker gear, and turn the motor over by hand a few turns to ensure nothing makes contact (without sparkplugs in).

It should then be safe to fire up the engine once everything else is together (prime the oil pump).

Good luck!