Rotax 912 and viking

[jrevens]

In my case - Hal Stockman installed the bigger balance tube on my engine. A little difference per side is nbd now.
That being said, I still checked the sync at the carb when I first got it running. It was close, and I did get it closer. I plan on checking it as needed or at every annual. I use my old motorcycle sync tool. It is four vacuum gages (I used two) you can adjust it to eliminate the pulsing to get a real smooth reading.

Not sure how accurate the measurement is, especially with the bigger tube downstream.
I guess if one was bound and determined to get the sync perfect, one could isolate each side with a gate valve on the big crossover tube.
Not sure if it's worth the extra time and effort. Tbh - how much closer could you get it?

Obviously, you MUST isolate the carbs from each other via the crossover tube to accurately synchronize them.

[Danilo]

Compare all-up installed weights carefully. Also, you'll be entirely on your own for an engine mount and cowling, unless Viking provide them for the Kitfox. The Kitfox factory does not support Viking installations. A Viking powered Kitfox might be a fleet of one; if others exist, I don't think they've appeared on this forum.

I was very excited about a higher horsepower automotive conversion when I started this journey. After doing a lot of research, reading this forum extensively and watching another builder with an auto engine (not Viking) get so frustrated that he removed it and sold the airplane, I changed my mind. I now have a 912iS in the garage, waiting for me to get off my butt and finish the airplane build.

There's one aspect of the computer-controlled Rotaxes that angers me. Rotax charges $2,300 for a locked down $70 off-the-shelf USB dongle (which is almost always out of stock everywhere) to download diagnostic data, and the detailed information needed to decode that data is unavailable outside authorized service centers. To me, that's the primary argument (beyond lower cost) in favor of the carbureted Rotaxes. Tuning and syncing carbs can be a pain, but you don't need eye-wateringly expensive tools and a factory authorized charge-by-the-hour iRMT to work on them.

If I had to make the decision again, I would likely do as Dave suggested: buy a used 912ULS, go through it with a fine-toothed comb, get the carbs and gearbox serviced, and maybe visit Hal Stockman for a big-bore kit. Cheaper, lighter and simpler.

I had at $26K check for a new Rotax 912IS that I brought in 2023 to Motive Aero after the CEO told me the price included the exhaust. After he confirmed while in front of him that the exhaust would not be shipped as I need to pay them another $3000, I stumbled upon a 0hr SMOH EDGE Performance built 912ULS for $11000! Thomas from Edge Performance built this engine to the point you can eat off it. Since I saved so much money I went ahead and bought their EFI and big bore kit. All in I'm about 20K for an engine that will be 20lbs lighter than the 912IS and 20 more HP!