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Old 03-16-2017, 05:59 PM
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rv6ejguy rv6ejguy is offline
Join Date: Mar 2005
Location: Calgary, Canada
Posts: 4,480

There is little mystery in this story. Once fuel is in a hot float bowl at atmospheric pressure, if fuel temperature exceeds the boiling point of the lightest fraction (usually Butane in winter mogas), bubbles result, those bubbles are pulled into into the main jet and you have a very lean mixture.

Winter mogas has about double the vapor pressure of summer mogas. This is a good reason to be careful using winter mogas on a warm day or at higher altitudes where pressure and therefore boiling point is lower.

Like I said, some winter gasolines will start to boil at just over 100F at sea level. That's easily exceeded on a heat soaked engine with carbs. Be aware that gasoline formulations are molded around the fact that most cars have been fuel injected for a couple of decades and EFI picks up cold fuel in the tank and pressurizes it before it reaches the engine. This drastically reduces the chances of vapor lock issues compared to carbs.

All this being said, mogas was not designed for aviation use. It may work fine if you're careful. Here is a good graphical representation of the vapor pressure variances in mogas vs. avgas:

Personally, it would give me the willies to run a carbed engine on winter mogas. I run it in my Subaru but it has EFI and I use up the winter mogas before it gets warmer. I've drained it out of the -6 and put it in my car on occasion because it wasn't safe IMO. I bought a Peterson tester when I switched from 100LL to mogas and that was pretty eye opening. There's a big difference between the 2 fuels.

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, Marcotte M-300, IVO, RV6A C-GVZX flying from CYBW since 2003- 420 hrs. on the Hobbs,
RV10 95% built- Sold 2016

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Old 03-16-2017, 06:39 PM
DHeal DHeal is offline
Join Date: Sep 2006
Location: Windsor, California
Posts: 680

Originally Posted by David-aviator View Post
And the springs driving to WOT, I don't like it.
The springs also serve to maintain a consistent tension on the two throttle cables.
David Heal - Windsor, CA (near Santa Rosa)
EAA #23982 - EAA Technical Counselor and Flight Advisor; CFI - A&I
RV-12 E-LSA #120496 (SV w/ AP and ADS-B) - N124DH flying since March 2014 - 640+ hours (as of June 2018)!
VAF donation through June 2019.
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Old 03-16-2017, 08:07 PM
PilotBrent PilotBrent is offline
Join Date: Dec 2011
Location: Hackettstown, NJ
Posts: 429

Many of us on occasion have experienced low fuel pressure warnings in the RV12/Rotax which I've seen described as a "Rotax gremlin". I've never had a rough engine in flight, but in warmer months I've experienced these warnings almost always when I pull back on the throttle to reduce altitude usually after a long cruise. These temporary low pressure readings eventually stabilize and the pressure recovers, but obviously it really gets your attention. Last spring it happened one time when I was defending over NYC at 8,000 ft and boy does your heart rate go up until it recovers.

Can't recall ever experiencing these events when I've had at least some 100LL in the tank. I almost religiously avoid using 100LL, but with spring approaching I think its prudent to mix fuels for upcoming flights until I'm sure summer blends are available at the local ExxonMobile station.
Brent Connelly
Hackettstown, NJ
RV-12, N913BC

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Old 03-16-2017, 09:57 PM
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DaleB DaleB is offline
Join Date: Sep 2012
Location: Omaha, NE (KMLE)
Posts: 1,838

Yeah... we've got a Young Eagles even this weekend, and I need to fill my tank. Think I'll mix in some 100LL just to be on the safe side.
Omaha, NE
RV-12 # 222 N980KM "Screamin' Canary" (bought flying)
Fisher Celebrity (under construction)
Previous RV-7 project (sold)
-=VAF=- 2017 dues paid
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Old 03-16-2017, 10:15 PM
jnmeade jnmeade is offline
Join Date: Mar 2013
Location: Iowa
Posts: 135

Originally Posted by AZLeeJay View Post
Most of these comments seem to support the new Swift unleaded avgas. I hope it comes to a FBO near me.
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