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  #11  
Old 03-15-2017, 04:35 PM
n233va n233va is offline
 
Join Date: Jul 2014
Location: Prescott, AZ
Posts: 16
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Both aircraft were flown out of Williams AZ this AM. Temps in the low 50's. No problems experienced. Both had fuel pumps running the other day. It is clearly a fuel blend problem. Winter blend in the states. Did not drain the tanks prior to takeoff and pressures remained steady.
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  #12  
Old 03-15-2017, 05:40 PM
AZLeeJay AZLeeJay is offline
 
Join Date: Dec 2013
Location: Phoenix
Posts: 92
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Thanks for the info Bob, I think I'll add a little 100LL next time I add some gas. Do you know when they change to the summer blend here in Az?
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  #13  
Old 03-15-2017, 06:45 PM
cactuspilot cactuspilot is offline
 
Join Date: Oct 2012
Location: Phoenix, AZ
Posts: 409
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May 1 is the final date for the refiners to switch and ship.

You might see it sooner.

I started topping off with 100LL whenever I can.

Burning 100LL will help with low fuel pressure warnings.
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  #14  
Old 03-15-2017, 08:05 PM
Boyd Birchler Boyd Birchler is offline
 
Join Date: Sep 2014
Location: IN
Posts: 85
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IF you can get it; summer blend (when it gets warm)91 octane auto "with out alcohol" is the best fuel for a Rotax. With alchol is next best. 100LL should be the last fuel of choice. Lead will cause problems with the starter clutch sprag, gear box, slipper clutch and in the Oil tank under the baffle. The engine is much happier without lead.
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  #15  
Old 03-15-2017, 08:21 PM
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AK4x4 AK4x4 is offline
 
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Location: PAWS (Wasilla, Alaska)
Posts: 129
Default Rotax fuel

The Rotax engines DO NOT like 100LL. They are very different from other aircraft engines, 92 or better octane premium unleaded with no alcohol is the preferred fuel. If you need to run pure 100LL always treat it with a lead scavenger, TCP or Decalin. Also with 100LL the only engine oil allowed is Aeroshell Sport 4 plus, and with 100LL you need to change the oil every 25hrs. If you exclusively operate with 100LL the gear box needs to come off sooner, 600hrs instead of the normal 1200hrs. Russ
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  #16  
Old 03-15-2017, 09:24 PM
RFSchaller RFSchaller is offline
 
Join Date: Oct 2010
Location: Phoenix, AZ
Posts: 1,919
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I've never experienced vapor lock in the 5 years I've flown my 12 in AZ including airports like Sedona and Valle and Williams in high country. What I have experienced is slight roughness when I pull back the throttle to descend and land. My engine has also developed a habit of starting and dying once before a second successful start. Full power and cruise are smooth as silk. I suspect a dirty idle jet, and I cleaned the carburetors during my ongoing annual. When I finally finish the annual it will be interesting to see if the issue is solved. If not, I guess I'll bite the bullet and pay to have a ROTAX shop overhaul them.

Rich
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  #17  
Old 03-16-2017, 06:51 AM
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Piper J3 Piper J3 is online now
 
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Location: Hinckley, Ohio
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Itís not the seasonal vapor pressure blend of the auto fuel, but rather the residual heat after engine shutdown that causes the fuel to boil off in the carburetor float bowls as I described in my post #10. Using 100LL doesnít fix the problem.

The RV-12 has a tightly cowled engine and when you shut it down the heat remains for a long period. If the engine cools and you restart at a later time Ė no problems. Cool fuel and cool carburetor bodies allow fuel flow with no harmful vaporization. Engine starts and youíre on your way.

What you have to watch out for is restarting a warm engine that has sat for some time. In this case there is likelihood that fuel has vaporized from the float bowls and the carburetor bodies are still warm. That is why it is best practice to allow the electric fuel pump to operate for approx. 5 minutes to recirculate cool fuel through the upper distribution manifold and return to the fuel tank.

I experienced this phenomenon just like others have. I was hoping rides with frequent start/stop and had the engine stumble on several occasions. I follow the hot-restart rule now and havenít had a problem. I run 93E10 auto fuel as recommended by Rotax. 100LL as mentioned in above post is undesirable in the 912 because lead spins out and deposits in the gearbox and also presents as sludge in the oil tank.

The only concern running unleaded auto fuel is the octane rating can be reduced if stored improperly or for long period of time. I use fresh fuel and fly often. I have an early model 12 and elected not to install the fuel tank vent. I stayed with the vented fuel cap which minimizes air transfer in the fuel tank when the plane is stored.

I didnít mean to write a book on this subject Ė just trying to keep us safeÖ
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  #18  
Old 03-16-2017, 07:03 AM
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David-aviator David-aviator is offline
 
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Location: Chesterfield, Missouri
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Quote:
Originally Posted by n233va View Post
Both aircraft were flown out of Williams AZ this AM. Temps in the low 50's. No problems experienced. Both had fuel pumps running the other day. It is clearly a fuel blend problem. Winter blend in the states. Did not drain the tanks prior to takeoff and pressures remained steady.
When I was flying with Subaru engines and mogas, I tested fuel before take off with the Hodges vapor tester, found winter blend way below safe flight reading one time and drained fuel.

At that time the Hodges tester was sold by Petersen with the mogas STC kits for various engines.

I found that ethanol eventually destroyed the tester, it had plastic tube. I called Petersen about it and he said he would consider having it made with glass tube but I don't think anything came of it. In fact I believe he stopped selling the tester, maybe because of liability issues.

I've considered running 91 octane mogas with the Superior IO360 180 HP engine but when I could not find another Hodges tester, it was factor to stick with 100LL. The other of course is the engine driven fuel pump, its internal materials probably are ethanol ok, like the AFP system, but manufacturers of fuel pump will not verify it.
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  #19  
Old 03-16-2017, 07:31 AM
Tomcat RV4 Tomcat RV4 is offline
 
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Location: Poughkeepsie, NY 12603
Posts: 143
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Sounds like another good reason to use Subaru with factory fuel injection controlled by
SDS FUEL/IGNITION CONTROL !
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  #20  
Old 03-16-2017, 07:36 AM
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DonFromTX DonFromTX is offline
 
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Location: La Feria Texas
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IF using Decalin or TCP, does that mean you can change oil at non leaded intervals, and none of the bad things from lead will happen to your engine?

Quote:
Originally Posted by AK4x4 View Post
The Rotax engines DO NOT like 100LL. They are very different from other aircraft engines, 92 or better octane premium unleaded with no alcohol is the preferred fuel. If you need to run pure 100LL always treat it with a lead scavenger, TCP or Decalin. Also with 100LL the only engine oil allowed is Aeroshell Sport 4 plus, and with 100LL you need to change the oil every 25hrs. If you exclusively operate with 100LL the gear box needs to come off sooner, 600hrs instead of the normal 1200hrs. Russ
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