disty issues?

85 gl 4x4 wagon i put an ea 82 out an 87 into and it runs fine but around 2500 to 3000 or so tach hops around.tried putting several other distys in and not running the one that works is a denso and the others ive been trying are hitachis. they were out of a car that fine but cap was left off outdoors for a few weeks anyway was wondering if i missed something or just have 4 bad distys

thanks for any help oh also when tach jumps it misses a little bit