Dude,
Had a very similar problem with my MC11 on it's first ride out post-crash (the crash was near you neck of the woods, on the A640 at the back of Scammonden going towards Huddersfield).

It kept losing power after a good thrash. One cylinder was clearly dropping out as every now and again it would kick back in. Luckily this only started to happen within 1/2 mile of home.

Might be related, but then again might not as the MC11 and MC21 share nothing except the v-twin configuration and nikosil cylinder plating.

I think on mine it is most probably fuelling. I haven't stripped the airbox or carbs since it went down the road, so it could have either eaten the filter element or knocked some of the sediment out of the botton of the carb and blocked the jet. Alternatively, it could be the ATAC valve as it is the front pot that is cutting out.

Haven't had time to check it out yet, probably get round to it one night in the week or next weekend. I'll post what was wrong when I find out.

All the best
philandhisjag