I put some Iridium plugs in my 94 springer and it ran rough. It even seemed to miss on acceleration every now and then.

I put my old plugs back in and it runs great

Has anyone had this problem before?

 

I've been running them for the last 2 years and have not had any trouble.

 

Have to ask... are you sure the gap was set properly?

 

The only thing that comes to my mind is iridium plugs seem to perform best with coil on plug systems. I don't know if your bike has a conventional coil system but if it does, that could account for the trouble.

 

Never had any issues w/em on my evo and not on my TC either. FWIW.
They come gapped already.

 

Check your gap just to make sure. Both of mine had to be gapped. Easy to do. I have never had an issue and have run NKG and Denso with great results.
Just thought of something...I wonder if the new plugs could be mis firing because of bad wires??? A buddy of mine had a bad experience with new wires, blaming the wires...it ended up he did not SEAT the ends of the wires to the BOTTOM of the connection holes, which caused them to arc...easy fix, pain to figure out. Bad wires might cause similar results. I have had bad wires in the past that looked fine...right up until there was any moisture in the air...doa.

 

I've had brand new, standard spark plugs be no good right out of the box. I can't think of any reason that the same thing couldn't happen with the Iridium plugs

 

All new plugs should have the gap checked. Any type of plug more than likely fits multiple applications, so they can't be gapped for any particular application out of the box. Also, all it takes is someone setting the box down hard in just the right way and the gap has been changed.

It only takes a second per plug, do it the correct way the 1st time.... all the time!

 

Had to gap mine.

 

I've installed hundreds of Iridium plugs and never gapped them. They even tell you not to because of electrode damage.
Iridium plugs are also intended for high output coil on plug and SPFI fuel systems. It only takes a little bit of excess unburned gas to make them miss.
And once the plug starts missing throw it away.