Moisture problems in unleaded fuel?

No, no current issues, as I mentioned to RW, I'm probably just being over paranoid. Before I found this forum I was reading quite a few others with various levels of "horror stories", especially vapor lock  during take off when running mogas in high temps after heat soaking on the tarmac for awhile. The iS is a bit intimidating to the uninitiated (like me) due to its level of sophistication & at least at first, what seems like a rather complicated power plant. I'm sure I will grow more comfortable with it as I become more familiar with its operation, idiosyncrasies & the like. I really appreciate the feedback and advice from you guys, thank you!

Hi again Mike

The iS is certainly not prone to vapor lock.  We do however have a general problem with auto fuels when they have winter blends (high butane content, high RVP numbers) and it is best to avoid this winter fuel in hot and high flying.  As a matter of safety it is always best to switch to AVGAS if you are going to fly above say 8000 ft.  Autofuels were never intended to operate at such low ambient pressures as we get flying this high.  This increases the risk of fuel boil off, vapor locking.  If you have good pressure reading instruments for your iS to read the delta pressure (do not use just a direct pressure reading on the injected) then you may see at high altitude the fuel pressure swings as the pumps cavitate when they get air in them with some auto fuels.   The same thing happens in carb engines also.  

Back to your concern on the crossover tube from ⅓ side to 2/4 side of the engine.  The iS flows so much fuel it should be just fine.  The fuel temperature will not heat in this area due to that same high flow.  

As for the shoulder months, most particularly the spring to early summer, you may want to switch to AVGAS.  it is fine if you want to mix AVGAS to MOGAS, they will blend just fine.  Dont worry too much about using AVGAS.  I personally think that if you are using AVGAS the use  of a fuel additive such as Alcor TCP or Decalin is a good idea.  They change the chemical deposits in the combustion chamber and soften any deposits that go into the oil. The lead that gets into the oil will seem like a slurry and not a hard paste.

Cheers

"If you have good pressure reading instruments for your iS to read the delta pressure"

Can you be more specific here? I'm interested in what this would look like.

hi Jason

To correctly read the fuel pressure on the iS engine you must use an instrument that has both an inlet pressure sensor and an outlet one.  The instrument has to have a way to interpret the signals relative to the airbox MAP readings.  The fuel pressure is relative, that is 3 bar or approximately 45 psi over MAP.  Given MAP constantly changes the fuel pressure must do the same to work correctly.  We must understand that the fuel regulator is mechanical in nature.  This then constantly has small over and under readings and is not locked on as some people think.  Fuel pressure is also not an electrical output of the CANBUS within the Rotax harness.  This is something that the instrument supplier must develop and work with the OEM.  Fuel flow that we see on the BUDS side of the output readings are calculated also, they are not measured.  

The most common ones have a sensor at the pump side of the engine and one near the pressure regulator.  Most will use the CANBUS MAP input and then they do the calculation as to the fuel pressure you are running.  Obviously as we most the throttle MAP constantly changes and therefore so does fuel pressure that has to be relative to the MAP. Each instrument supplier that i have seen that has fuel pressure has developed their own way to give you the reading.  If you are looking for an instrument then they would be the right people to tell you what sensors match their requirements and they should give you the location for mounting them in the system. 

Cheers

Thanks again RW. I'm thinking for Arizona winter flying, a 50/50 mix of 91E10 with 100LL and decalin. Do you think would be a safe bet? I'm in Northern Arizona so I fly at high altitudes alot. I have a source for 100E10 as well, do you think the higher octane would help even though it's still got ethanol in it? Also, will the decalin keep the lead build up off the valve seats? Also, the pressure readings you refer to (delta and direct) is this the same fuel pressure reading I get on the Dynon? Sorry for the low brow questions, I'm just not that up on alot of this stuff yet......?