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pete(at)flylightning.net
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 Posted: Sun Jul 01, 2007 2:29 pm Post subject: Float Valve Issues |
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Every month I get a call or two about float bowls overflowing and engines running too rich from too much fuel in the carb bowl. Most of the time the cause is a small piece of rubber debris that hides inside the rubber fuel hose after it is cut to length. Only at some future time does it work its way down to the float valve. We have also found small pieces of dirt that found their way into the line after it was dropped on a dirty shop floor.
John Jenkins was kind enough to send photos of the debris he found. The email he sent and my response follow below:
| Quote: | At WOT and about 200' at the end of a short runway this morning all of
a sudden the 3300 began missing like crazy. I looked for a field to set
down on and pulled back some on the throttle. The missing stopped and I
was climbing at about 500 fpnm so I kept on going back to C29,
beginning to smell fuel about 5 miles out. Landed ok and a mechanic ran
out to say he could see I was running very rich.
We pulled the cowl and fuel was running down the firewall. Turned out
that fuel coming into the airbox from the little hose at the top of the
carb. I didn't run the engine again, but got this result by turning on
the electric fuel pump. Not leaking anywhere else.
Any idea what's going on? Jj
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My response:
| Quote: | My guess is that the float valve is stuck open for some reason and not
shutting off the flow when the float bowl is full. The symptoms would
be rich running and fuel running out the bowl vent (clear hose from
carb to airbox).
It might be a piece of dirt or might be a valve body problem (there is
a small spring in the valve body) or floats that have failed (very
rare)
Pete Krotje
Jabiru USA Sport Aircraft, LLC
|
John’s return email with photos:
Pete, you hit it on the head. At first I found nothing. Then I put some hose on the fuel inlet and blew lightly. Clogged. Blew harder and you can see what appeared in the valve seat. I'm including another photo to show the size of the shard.
I hope I've learned my lesson. Thanks for the help. jj
Jabiru USA would always suggest blowing out the fuel hose after cutting and after hooking up the fuel system to flush a quart of fuel through the system before starting the engine.
Pete
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Peter H
Joined: 20 Mar 2007
Posts: 197
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| Posted: Sun Jul 01, 2007 9:52 pm Post subject: Float Valve Issues |
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As a matter of interest I have taken a number of test readings measuring fuel flow rates with a Navman flow meter. The tests were conducted near WOT using the float needle seat 2.25mm as supplied by Jabiru, and also with the 1.5mm seat as recommended by Bing.
Even when using the Bing recommended HP seat, when the boost pump is turned on fuel flow immediately increases by approx 5 LPH and EGT comes down from about 750 deg C to 650DegC. These carbs seem to be very sensitive to fuel pressure and I think they would probably work best with gravity feed.
Peter
From: owner-jabiruengine-list-server(at)matronics.com [mailto:owner-jabiruengine-list-server(at)matronics.com] On Behalf Of Pete
Sent: Monday, 2 July 2007 8:27 AM
To: jabiruengine-list(at)matronics.com
Subject: FW: Float Valve Issues
Every month I get a call or two about float bowls overflowing and engines running too rich from too much fuel in the carb bowl. Most of the time the cause is a small piece of rubber debris that hides inside the rubber fuel hose after it is cut to length. Only at some future time does it work its way down to the float valve. We have also found small pieces of dirt that found their way into the line after it was dropped on a dirty shop floor.
John Jenkins was kind enough to send photos of the debris he found. The email he sent and my response follow below:
| Quote: | At WOT and about 200' at the end of a short runway this morning all of
a sudden the 3300 began missing like crazy. I looked for a field to set
down on and pulled back some on the throttle. The missing stopped and I
was climbing at about 500 fpnm so I kept on going back to C29,
beginning to smell fuel about 5 miles out. Landed ok and a mechanic ran
out to say he could see I was running very rich.
We pulled the cowl and fuel was running down the firewall. Turned out
that fuel coming into the airbox from the little hose at the top of the
carb. I didn't run the engine again, but got this result by turning on
the electric fuel pump. Not leaking anywhere else.
Any idea what's going on? Jj
|
My response:
| Quote: | My guess is that the float valve is stuck open for some reason and not
shutting off the flow when the float bowl is full. The symptoms would
be rich running and fuel running out the bowl vent (clear hose from
carb to airbox).
It might be a piece of dirt or might be a valve body problem (there is
a small spring in the valve body) or floats that have failed (very
rare)
Pete Krotje
Jabiru USA Sport Aircraft, LLC
|
John’s return email with photos:
Pete, you hit it on the head. At first I found nothing. Then I put some hose on the fuel inlet and blew lightly. Clogged. Blew harder and you can see what appeared in the valve seat. I'm including another photo to show the size of the shard.
I hope I've learned my lesson. Thanks for the help. jj
Jabiru USA would always suggest blowing out the fuel hose after cutting and after hooking up the fuel system to flush a quart of fuel through the system before starting the engine.
Pete
[quote][b]
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