A bit of technical info useful to all twin spark oilhead riders.
I just had a failure of a primary cap/coil, the unit on the end of the primary spark plug that needs the special tool to remove. There is a coil system inside that cap, and mine just failed after changing the plugs. Cost $200 to replace each one. See the following :
I had the same issue this year on a customer's bike. The coils themselves are still in a closed circuit not allowing the gs911 to indicate a problem (Meaning not actually burned out). The real failure area of these coils?
The connection between the discharge end of the coil and the spark plug connector. I had the exact issue and once i physically disconnected the coil the end stayed on the top of the plug. Ordered two new coils and she pulled strong as a horse again!
Its been my experience anyone running a Oilhead should keep a spare if your a long distance rider. I see these fail about 75,000KM, its the heat that kills them actually.
So, it appears that the coil system separates from the plug connection when the plug cap is removed, this explains why mine failed when I replaced the spark plugs on a 50K service. So, the lesson is : if you notice your bike running like a pig after putting new spark plugs in, it is probably a failed cap/coil and beware, BMW do not carry these in stock
Benefits of twin spark though are that on such failure, the bike still works, then again on a single spark bike you don't have these parts that are likely to fail.
Just FYI
Geoff