Hi Martin,
I've been playing with, and flying, fixed compression for decades. Could I make a few respectful comments...
1. I've read all sorts of conjecture concerning fuels... There'sno need to get bogged down in assessing variousfuel mixes... Just make up the recommended Drone fuel 75/25 (this was the original Micron recommendation, in 1943). This fuel will be OK in any temperature between about 20°C and 30°C. Below 20°C (unlikely in Fla.), you may need a bit more ether (80/20 is OK because inthe lowerambient temperatures, you won'tbe overheating). Conversely (andmore likely in Fla.), above 30°C, if you don't reduce the ether content slightly, you'llget pre-ignition (combustion will occur before TDC), which results in very rough running and vibration. IMO,this is why some people find that Drones vibrate, they just have too much ether in the fuel. So in the high temperatures that you have in Fla., in summer, you may well do better with 60/40 fuel, or even 50/30 with 20% kerosene. Personally, I always use 75/25 and just avoid using the engines in very high or very low temperatures (otherwise, you're continually messing around changing things).
2. Your NVA issue is a non-problem. Just borrow one that fits (no air leaks and with the hole roughly in the middle of the venturi) from another engine. In the States, I think the old Austincraft "universal" NVA would be an excellent solution.
3. Concerning the photo you've posted. If you've never run that engine before, and you're not experienced with fixed compression, then the prop on the engine looks to be far too small. To run a Drone/Micron etc. for the first time, always start with a 14x6 wood prop (another Micron and Drone recommendation!). When you get used to the engine, then you can start to experiment with other props. TheTopflite 14x6 wood is great for flying old timer RC so, for me, there's not much point in playing with smaller sizes, it just complicates the issue and would only be relevant if you intend to fly CL...
4. One potential issue is that we're communicating internationally, and between very different climates. Fixed compression diesels are very "temperature dependent", and opinions that are valid in one part of the world won't necessarily be valid elsewhere. In the warmer temperatures of the southern US, there shouldn't normally be any problem running fixed compression. However, in cold climates (Alaska, Norway, etc.), there probably won't be many days in a year on which a FCD will start easily and run well... One "advantage" of being in Europe is that we're half-way between these extremes. We get both types of climate, so I see those changes in running characteristics, twice, every year!
Brian