Congratulations on getting a Kitfox.

To answer your question regarding fuel to use with the airplane, I am not sure what a 958 is but from your pictures it looks like your airplane has a 2-stroke. Probably a Rotax 582. If that is the case, you would be best running ethanol free mogas. Alternately, you could run 100LL with the Decalin fuel additive which scavenges the lead preventing lead buildup issues. I have had two Kitfoxes powered by the 582. On the first it had fiberglass wing tanks and I ran 100LL with Decalin. It ran just fine like that but I didn't have that one very long. Probably put about 50 hours or so on it is all. Currently I have a different 582 powered Kitfox but this one is a hybrid with a Kitfox 3 fuselage and kitfox 4 wings and mixer system. As such it has the 10 gallon plastic fuel tank between the instrument panel and firewall. Because of this I have been running premium auto gas with 10% ethanol because there isn't a gas station for about 40 miles from me that has ethanol free. It also has a 6 gallon fiberglass wing tank and that tank will only see ethanol free fuel, either 100LL + Decalin, or ethanol free mogas. It runs great. Rotax recommends auto fuel for these engines and they approve up to 10% ethanol. It is really the rest of the fuel system that dictates what you can put in them.

If the airplane has the fiberglass wing tanks, given the vintage of the airplane, it probably doesn't have the newer ethanol resistant fuel tanks, so stay away from anything that has ethanol.

If you are not familiar with operating 2-strokes, a tip is that the EGT gauge is your friend. 1200 is max EGT and you don't want to exceed this. Stock jetting isn't the greatest at the low end. Rotax says 55 idle jets but I currently have 40s in and it runs much better. Also the stock needle has a lean spot in the midrange, so I switched. I can get you the part number later. The jetting chart is a little rich at the top end but is safe for EGT so I run stock jets dependent on weather conditions. I also run a homebrew mixture control that I can use to lean the slightly rich condition a little. The "Hacman" mixture is essentially the same as I have.

Getting back to operation of the 2 stroke, here are some bullets
  • After start idle about 2400-2500 until the water temp reaches a minimum of 140 deg F. DO NOT apply high power until it is at least 140. It should only take a few minutes, and if it takes a long time you should check to make sure a thermostat is installed in the engine. The first 582 Kitfox I had did not have a thermostat when I bought it and it was a pain until I discovered it and put one in.
  • After warmup the engine should idle down to 2000 rpm or below without quitting. May be rough, but should not quit. If it doesn't smooth out until 2200 rpm or so that is ok. This is where the idle jet is too rich. With the stock 55, mine would not idle below 2000 and was rough til about 2300. with the 40s in it will idle smooth down to about 1800 and I can go even lower but don't need to.
  • In flight, keep an eye on the EGT. I had a Westach dual EGT and it was way off. I wound up putting in an automotive dual digital EGT but I like it much better. Had to weld in some bungs for the EGT probes but it is better IMO. My egt runs around 1050-1100.in cruise.
  • One area you need to watch the EGT in particular is powered descents. When the prop unloads under power the EGT goes up and depending on conditions can go over 1200. I still make powered descents but keep an eye on EGT and adjust accordingly. Another option is to "chop and drop" where you pull power off enough that there just isn't enough going on inside the engine to get too high on EGT.
  • If EGT consistently runs high or low you can adjust some by adjusting prop pitch. More pitch lowers EGT while less pitch raises egt.


All this may sound complicated but it isn't really once you get used to how the 2-strokes operate. It is a matter of understanding the engine and how it needs to be operated.