Fuel flooding and v...
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Fuel flooding and vapour locks

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Joined: 5 years ago
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Hi, I'm on my 5th jabiru engine and all have had fueling problems.  Some of these have caused aborts, others have caused emergency landings. Some resulting in damage.  Flooding seems very common and has happened on all at one time or another.  Is there any reason why Jabiru do not mandate a fuel return line as per the Rotax Mandatory safety notice? - https://www.rotax-owner.com/en/flightsafety/476-ai476

Issues I've had, this can't be normal...:
  • Thruster1 - Suspected vapour lock. Loss of power after take off causing precautionary field landing near Swansea airport. Minor damage.
  • Thruster2 - Fuel flowing over the screen during taxiing - seems common, all usual causes investigated. 
  • Thruster2 - Suspected vapour lock shortly after take off, loss of power. Emergency landing at airfield, aircraft damaged.
  • Jabiru1 - Fuel overflowing the float bowl - again too common.
  • Jabiru1 - Suspected fuel lock causing loss of power on take off (shortly after my ownership, during my mentoring of new owners). No damage.
  • Jabiru2 - Fuel flooding from cowl, on inspection from float bowl after landing.
  • Thruster3 - Fuel spilling out of pressure compensation tube during taxiing, covering lexan screen.


As you can see - I'm loyal, but these consistent fueling issues are a worry, especially as suspected vapour lock totaled my Thruster2 last summer. 250ft ato and sudden significant loss of power. 

I'm an Engineer, I'm aware of all the usual suspects, fuel pressure, float needle/spring, floats absorbing, float level setting, airbox siphon,  etc.  I try never to operate the aux pump until take off roll or landing.

If Rotax issue the mandatory safety, why has Jabiru not considered the same setup?  Thanks in advance.


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Joined: 3 years ago
Posts: 171

Hello Hobson,

Thats a bad run you are having there!  Our experience here is that vapour lock is very uncommon in Jabiru Aircraft, almost unheard of. So there must be something with the thruster fuel system.  The jabiru runs low fuel pressure (below 4psi) so it is a possiblity with a hot fuel line or on the suction side. 

As far as the flooding - fuel running out of bowl etc, that is almost always due to excessive fuel pressure.  The only way to tell, for sure, is to put a fuel pressure gauge in the line between the engine driven pump and the carburetor.  On later 4 cylinder engines we have been putting a small float valve to allow it to tolerate higher pressure.  Unfortuneatly this isn't possible on the 6 cylinder.  

Hope this helps.

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