Have you gotten an honest 'fighting weight' for the R1200? Would the Yamaha RX1/Apex/etc be in the same ballpark? There are already at least two vendors offering drives for the Yamaha 4cyl engines, and Air Trikes says that it will be the next engine they build for. There seem to be a *lot* of them flying here in the USA on STOL a/c and trikes, and I haven't read anything negative from anyone who's installed one.
The Yamahas make more HP than you're looking for, but if they're light enough (and they're really light), you might be able to just let the engine 'loaf'. Another option would be the 3 cyl version; only a little lighter than the 4cyl but might be enough to matter in your case.
Charlie
Having done a BMW R1200GS and recently, a Yamaha Apex conversion, I am here to say the Yamaha beats the BMW across the board...hands down. Lighter, simpler, less expensive, more efficient.....and more reliable, among other advantages, such as more power and way better throttle response. Also easier to get official maintenance manuals and parts for the Yamaha, and an R1 bike guru (the Apex's internals are from an R1) did the rebuild for us at the local Yamaha dealer. BMW flatly refused to give advice or do service due to insurance reasons, and we were stuck with using bootlegged manuals, as only certified repair centers can have the latest & greatest.
The expensive BMW experiment of ours a few years ago ended with a failure of the integral gearbox on the dyno during a simulated max power climbout...about 45 seconds into it to be exact. Total time on overhauled/modded engine? 1.3 hours. The cause of the failure was insufficient lubrication in the gearbox as a result of the lube system modifications. We were in about $5,800 at the time of failure. On the record, we were not abusing the plant on the dyno at all.
The Yamaha conversion was simple as it could get. Bolt on the SkyTrax box and replace the wire loom & exhaust system. The plant ran like a dream on the dyno, and we have a baseline vibration spectrum profile on the entire system (vibe spectrum analysis is a key part of our test program).
Our Apex YG4i with SkyTrax box is now preserved, but otherwise ready for install on our bird when the time comes!
There is even an advantage in an anticipated lower insurance premium for us with the Apex!
