R1200S Misfire troubleshooting - Bristol

[Keith_P]

2 plugs per cylinder is a bit of a pain to diagnose when you've got a misfire! Thought I'd sorted it with new plugs - possibly only one needed - but it's back after 1 ride, so I'm thinking coil pack... It's only done 11500mls, so can it really have a failure(s)? I'd like to find a local repair place to do swapsies before I shell out on what would have to be 2 x lower & one upper coil pack!
Oh, yes, the injectors are squirting ok and I've got what look like good sparks in fresh air...

[Humbug]

You can isolate the coil by unplugging them in turn. The bike will still run with one spark missing but not two. Pull a coil and start the bike, If it runs, the coil you have pulled is bad. If it doesn't run, its one of the other coils. Yes, it can happen at that mileage. Another issue that will cause the bike to cut out is the valve adjustment. If the bike cuts out or runs badly at idle it could be that they need checking.

[Keith_P]

Thanks Humbug. Yes, I wasn't thinking clearly about the 2 plugs per cylinder being harder than one! Valve clearances are ok - the misfire is very abrupt, hence my strong feeling that it's electrical. Will also check all earthing points for corrosion, especially the ECU.

[ianbcr]

Usually a bad earth gives you the symptons of a flat battery and just get a clicking from the starter button. Had this with the bcr but ran fine from a bump start but cleaning the earth to frame cured the clicking and all back to normal.

[Keith_P]

Thanks - right on track as I'm getting that first stab click from the starter, then all ok on the second go (new battery made no difference).
I started up with 1 plug per side this evening, then the other two plugs and it's running perfectly like that and (not surprisingly) with all 4.
Earth connection now #1 culprit, especially as this bike had a load of corrosion evident when I bought it...

[Keith_P]

Well, the main earth point was a challenge to 'service' without removing the tank! Good enough tho' until I have it all apart one day. Definitely improved matters - fingers crossed that my misfires have gone...
Thanks for the suggestions