Motorcycle Repair: running rich?, air fuel mixture, intermediate jet

Question
Mike

I put a new S&S Super E on my '82 shovelhead last summer. Otherwise the bike is stock. The intermediate jet is 0.295, main jet is 0.068, idle mixture screw is 1-1/4 turns out, and throttle pump is 2 turns out.  It runs pretty good, but the plugs eventually turn black and it backfires in the pipes and idles rough after a cold start using the choke.  I get a little black smoke when I blip the throttle. There is no backfire with clean plugs and warmed up.

Is it too rich?  If so, should I start with turning in the idle mixture screw?  Is there any risk of permanent damage by running rich for a long period?  Also please recommend a spark plug and gap.

Thanks

Answer
Sorry I didnt get back to you sooner. WE had a heck of an ice storm so no power, no heat, no sump pump and no computer!
Now to your problem. Sounds like your running rich. change your intermediate jet to a .028. Start the bike and let it warm up. Turn the the throttle pump off by screwing it in. Set the idle mixture screw by slowly turning it in. When the bike starts to stumble, turn it out 1/4 of a turn.
Now go for a ride. Gently go through the gears, not going over 3000 RPMs. You bike should be smooth. If it bogs, like not enough gas then go bigger on the intermediate jet, if it spits, like its getting to much gas then the intermediate jet is to big. If you have to change jets, always reset the air/fuel mixture screw.
One you have the intermediate jet set, not go back and do the same thing for the main jet. Start with the .068 that you are running. Now go for a test ride, but stay at RPMs over 3000. The bike will stumble when you are changing gears because your pumper is closed, so dont worry about that.
once the jets are set, now set the pumper. Turn it out around 1.5 turns and go for a ride. Go through the gears like you were passing somebody. If the bike stumbles turn it out about 1/4 turn. Keep doing this until you stop the stumble.
As to the spark plug. Spark plugs are personnel preference. I use Champions. The gap would be .040 for an electronic ignition.
Good luck and happy riding
Mike