Johnwebley, there may not be much of an audience for it though. Also in a competition for Honda general knowledge I'd be soundly beaten by some of the others on here.
Zippy, the Imp looks nice and is after all a SOHC so it scrapes through ok on that front. Must be one of the most diverse motors around though as I've seen them in both solo motorcycles along with quite a few road race outfits in the past, this along with their four wheel applications of track and extensive rally use must cover many forms of motorsports.
Seeing the installation like that and proximity of the chassis leg got me thinking more about suitable carbs. If you take a 900/1000cc bike motor as a good source, then something like the original Yamaha 1000 Exup has a similar potential to the Honda 900 carbs but the whole bank of carbs is tilted up at 45 degrees as the bike cylinder install was lent forward at that angle. This means the carb intakes would possibly be above and clear of the chassis in your use so may offer something useful in the way of suitability.
Thinking further about your setup as it is, it may be realistic to make up some bespoke needles for the carbs with a slightly smaller diameter at the thick end of the needle to bring the lower throttle opening mixture a little closer to the topend to give a more linear progression to work with.
As you say, it's interesting to work through something like this anyway with the satisfaction if you get get good progress.
