I have a 03 SERK with a 103 engine that has a stage 4. When I was at the dealership, I asked for some spark plugs. The gave me P/N 32186-10 Screamin Eagle plugs gaped at 0.035. The plugs that I removed were HD 6R12. There gap is .040.

The bike seems to run about the same but I'm concerned that it may damage something. Should I change back to the HD 6R12?

 

The plugs you removed are the same as in my 2011 Sporty! If you check your service manual it should tell you the correct spec, in Section 1. As you have an SE engine, the SE plugs sound right to me, but well worth checking. If you are servicing your bike yourself and don't have one, the factory service manual is a mine of useful info!

 

The manual calls for the 6R12 so I'm not sure why they gave me a different plug. I didn't look up the number before buying them. Maybe the SE plugs are a better quality but I would think the gap would be the same. I put in a call to the dealership for info. Thanks for responding.

 

There was a time in my early riding career when getting the correct spark plug seemed far more important than it seems to be today. The difference in gap may be down to differences in resistance between the two designs.

According to the SE catalogue, those SE plugs "Fit ’99-later Twin Cam models, ’86-later Xl and Xr models, and evolution® 1340 models equipped with Screamin’ eagle performance Cylinder Heads." so they sound like a good choice, bearing in mind your stage 4. Perhaps your dealer was on the ball after all! If they came gapped to .035 I would leave them like that personally.

 

I buy all my plugs for 42 years for my Harley s at the auto parts store as the are much cheaper.