Unless all of the linkage levers are returning to the 'neutral' position (all aligned with each other), you will not be able to shift into other gears (by design).
My linkage levers were binding on each other to such an extent that shifting was hard. The solution was a clean & lube.
See:
http://www.peachparts.com/shopforum/showthread.php?threadid=78715&highlight=shifter