we have a 96 dyna FXDWG and have ignition problems at idle, the rear cylinder misses at a idle. whenever the bike is wet, raining, or on a humid day. The rest of the time it seems to run great. We have a Crane high 4 single fire street race ignition and coil. What can cause this problem? When we throttle it up, the miss goes away.

 

Sounds like a bad spark plug wire. Maybe a plug as well.

 

+1 with the plug, plug wire but go one step further a possible intake manifold on the affected cylinder. Not a big leak but enough to affect idle.