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jeffrey-j-paris(at)excite
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 Posted: Sun Apr 06, 2008 1:24 pm Post subject: Fuel Pressure Question? |
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Dear Jabiru Engine Wonks,
I have a question about fuel pressure and fuel flow. I currently own and fly a Zenith CH601XL equipped with a Jab 3300, I have about 192 hours on AF/PP. I am fortunate in flying with a fully TSO'd Xerion Auracle Engine monitor/analyzer. My two last flights I have noted some peculiarities with fuel pressure and fuel flow while flying.
My engine analyzer at altitude sends up a warning message that fuel pressure is low/lowering and while all seems to be running right I noticed that my fuel flow numbers were going up? When I turn on my Facet boost pump the fuel pressure would go back into the normal green values and the fuel flow returns back to a respectable number.
Furthermore, while flying on the way home my engine analyzer started this curious behavior again. While slowly descending into my home airport I reduced power and watched everything come into sync. What got my attention next was that I felt the engine sort of "burp" or skip a bit. I pulled carb. heat and turned on the boost pump to cover my rear end. It was enough of a "burp" for me to take notice.
So with that information in hand, what does this mean? You would think that low fuel pressure would = lowering fuel flow right? Conversely, the opposite should apply ... Does anyone here know what I'm dealing with other than that she's running beautifully.
Thank you for you time and consideration.
Jeff Paris
N196ZP KSDC Williamson-Sodus
CH601XL Jabiru 3300
_______________________________________________
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Peter H
Joined: 20 Mar 2007
Posts: 197
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| Posted: Sun Apr 06, 2008 1:46 pm Post subject: Fuel Pressure Question? |
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Jeffry
I have spent some time investigating the fuel flow of my J3300 and found as
follows:
The needle valve seat provided by Jabiru is 2.25mm and is meant for gravity
feed. It leaks from about 2700 rpm causing the fuel bowl to get above design
level and the engine to run rich . Excessive rich running causes decreased
power and rough running very noticeable if it occurs in flight.
The correct needle seat for a fuel pump fed installation is 1.5mm and I
fitted one of these. It ran too lean at WOT but when I started the boost
pump it also leaked and I saw 36LPH on my Navman fuel flow meter.
I have discussed this issue with the Jab engine shop and understand that the
setup is tuned for the typical Jabiru installation and that needles and jets
were chosen to provide best cruise mix at about 2750 and excessive rich mix
at higher RPM and at WOT as a measure to ensure the valves are kept cool.
It may possibly be that you are experiencing patchy over rich running.
Peter H
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craig(at)craigandjean.com
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| Posted: Sun Apr 06, 2008 2:35 pm Post subject: Fuel Pressure Question? |
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Where is your fuel pressure sender? Between the mechanical pump and the
engine? If so think of it this way: with a pump working against a dead-end
pipe you would have the maximum pressure and no flow. As soon as you allow
fuel to flow the pressure will drop and the flow rise.
-- Craig
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info(at)jabirucanada.com
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| Posted: Sun Apr 06, 2008 3:03 pm Post subject: Fuel Pressure Question? |
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Dear Sir:
I'm sorry but the two people that could help you, are in Florida at
the Sun & Fun air show. They should be back on April 15. Stan or
Gord will email you as soon as possible.
Yvonne
At 05:18 PM 4/6/2008 -0400, you wrote:
| Quote: |
<jeffrey-j-paris(at)excite.com>
Dear Jabiru Engine Wonks,
I have a question about fuel pressure and fuel flow. I currently
own and fly a Zenith CH601XL equipped with a Jab 3300, I have about
192 hours on AF/PP. I am fortunate in flying with a fully TSO'd
Xerion Auracle Engine monitor/analyzer. My two last flights I have
noted some peculiarities with fuel pressure and fuel flow while flying.
My engine analyzer at altitude sends up a warning message that
fuel pressure is low/lowering and while all seems to be running
right I noticed that my fuel flow numbers were going up? When I
turn on my Facet boost pump the fuel pressure would go back into
the normal green values and the fuel flow returns back to a respectable number.
Furthermore, while flying on the way home my engine analyzer
started this curious behavior again. While slowly descending into my
home airport I reduced power and watched everything come into
sync. What got my attention next was that I felt the engine sort of
"burp" or skip a bit. I pulled carb. heat and turned on the boost
pump to cover my rear end. It was enough of a "burp" for me to take notice.
So with that information in hand, what does this mean? You would
think that low fuel pressure would = lowering fuel flow
right? Conversely, the opposite should apply ... Does anyone here
know what I'm dealing with other than that she's running beautifully.
Thank you for you time and consideration.
Jeff Paris
N196ZP KSDC Williamson-Sodus
CH601XL Jabiru 3300
_______________________________________________
Join Excite! - http://www.excite.com
The most personalized portal on the Web!
--
Checked by AVG.
4/5/2008 7:53 AM
|
Lancaster Aero Ltd.
PO Box 56
Bainsville, ON K0C 1E0
Tel: (613) 347-3155
Fax:(613) 347-3074
Email: info(at)jabirucanada.com
www.jabirucanada.com
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