My primer gets sticky now and then.  I suspect the orings are getting old and hard and the plunger gets slightly gummy.  I put a little WD40 on a paper towel and clean off the plunger.  Seems to work for quite a while.

Addendum to my previous post...... If the primer O rings are worn or hardened they should be replaced. A leaking primer can cause an excessively rich mixture and higher than stated fuel consumption. After replacing the O rings coat them with a light coating of fuel lube.

What specifically is "fuel lube" and where can you get it.  I saw nothing by that name in either the aircraft spruce or chief catalogs.
thanks, joe