Get a Harley service manual if you don't already have one. If you are convinced it electrical there will be a detailed layout in the manual. Start at the beginning check battery, ground etc. and work your way to coil and plugs. It usually something simple. The Harley wiring harnesses are usually extremely good. If someone has messed with or replaced stock items that is usually the problem.

Take it to a Evo or Harley shop you trust give em a few hours time and pay see what they come up with if you get stumped. Again they tend to run forever if you replace the inner cam bearings and rebuild or replace the carbs.

Good luck, you will get there.

 

 

Hope you got it fixed with the new plugs...

If I may be so bold as to offer a little advice....

Get the Harley Service, & Electrical Diagnostic Manual. Some old ones can be purchased new, or you can usually find used ones on eBay. They won't be cheap, but will pay for themselves in short order. I also get the parts manual... the exploded parts diagrams help me a lot, as I'm a visual learner... If you have, or can read online, the owner's manual for your bike, it will list the HD part numbers for those manuals in the back.

Also, not sure what you mean by "BMW mechanic guy", but I'm gonna guess you're not a BMW Factory Tech, working in a BMW shop... Day one vehicle repair, is to diagnose the problem first, then replace the bad part(s)... just throwing parts at a problem can be an expensive, long process. Unless you get real lucky.... it's not a good way to try to fix a problem. I've never known a BMW shop to work that way.... In any case, the above manuals can help you with your trouble shooting and reaching a proper diagnoses...

Once you getting running well, you should love that bike. My EVO was trouble free and maintenance only, for the 60K miles I owned it...

 

One thing i didn't mention was my 98 had sit for a while before i bought it and the gas tank had rusted, it ran awful until I had it coated once again.