Jaques,
I had to remove the 914 manual from this attachment.
You probably already downloaded the 914 repair manual.
Regards,
Bud
----- Original Message -----
From: Bud Yerly<mailto:budyerly@msn.com>
Sent: Sunday, June 10, 2012 5:14 PM
Subject: Re: Europa-List: RPM drop with a 914 above 100%
Jacques,
Sounds like you have an excellent knowledge of the 914 systems. I am
having a run of the same problems.
We will be putting in a product deficiency report but essentially, if
the turbo controls are all working, it is the carbs/fuel delivery.
Bob Borger is suffering through a slightly different problem but close,
as does Homer Baker, and I have two 914s that had me pulling my hair out
with similar symptoms.
Here is a summary of what to check:
If the engine starts to die as the boost comes on, most likely the carb
float bowls are leaking.
Ed and I were pulling out our hair and are going to put in a product
deficiency report. I just did a bunch of work on a 914 because the carbs
had never been rebuilt over 300 hours. We put in a carb kit and it
worked great on the ground but at altitude were not able to get it to
perform as the engine began to sag and miss.
Final answer was to soak the paper float bowl gaskets overnight to get
them to swell and seal. Then you fly away and after the engine has set
a couple weeks, the gasket dries out and the leak reappears. Rotax now
uses a rubber gasket for the bottom of the bowl, which affects the
torque on the bolt on the bottom of the float bowl, and if memory serves
the torque is low at 48 inch pounds, and the rubber gasket, once
squished, gets some gas on it then it dries out and the bowls are loose
again after setting a bit. I don't mean to sound angry, just being
frank.
As to troubleshooting:
First: I prefer to hook my computer up and check my sensors and
throttle position and waste gate operation. You should not need the
computer, you only have to check on initial power the wastegate moves
with the self test. Next check that the cable is pulled almost fully
tight at idle. Note as the throttle is moved half way up, the waste gate
cable is let out and the spring opens the gate about half way (45%
really), then at full throttle it pulls the cable back. If it does all
that, it's basically OK. If it doesn't, we need to look more.
Symptoms I have seen for fuel related problems:
Providing the idle is fine and carbs will balance:
As the engine runs up, the waste gate goes from nearly fully closed
(your cable on the waste gate servo is fully pulled) and moves at half
throttle position
to about half way. The boost kicks in and the MP goes up from about
12-14 at idle to about 30 at 4000. As the boost comes up, any leak in
the carbs or the system (all that tubing) will lean the engine out and
it will not produce power. So the RPM stagnates and the engine dies if
the boost goes up much above atmospheric.
I have only one carb leaking and it is running rough as the boost comes
on. Once the gasket gets wet, it seals up a bit and runs fine. I swear I
will proseal the carb on if the cork gasket doesn't work. If both carbs
are leaking then the engine stays fairly smooth, it just cuts out at
altitude.
Be sure to check your pressure lines on top of the engine for cuts,
leaks etc. I use a vacuum hand pump to check each system once
disconnected to its sensors of course. You don't want to break anything
or put vacuum to a pressure sender.
Next, your fuel pump or pressure regulator may be malfunctioning. Easy
to check. You have a fuel pressure gauge, you only need to get a boost
gauge or old time fuel pressure vacuum gauge combo to tee into an airbox
pressure line. If you have a split fuel differential pressure gauge you
have to unplug from the differential sender and plug into the airbox
pressure line a fuel manifold pressure gauge with up to 50 inches of
boost (2 inches HG is about 1 psi pressure), a boost gauge, or the old
time vacuum fuel pressure gauge to the airbox hose. Turn on the master
and note the static pressure of the fuel pump with engine stopped. It
should be 3.5-4 PSI minimum with the pressure regulator attached as
normal. Pinch off the fuel return line by bending it slightly and the
pump pressure should run up even to 10 or 12 PSI. Do not hold the return
hose crimped long, as you don't want to fail your regulator. If the
pressure is OK, the pump is good. Check both the main and aux pumps. If
you see no increase in pressure, it is the pump or fuel pump setup is
wrong with the check valves. Note if one or both of your carbs is
leaking fuel out of the float bowl. Next check the inside of the carb
by loosening the airbox and checking for fuel draining out of the carb
and filling the carb and airbox. If fuel is draining out when you
remove the airbox from the carb face, then your float valve seats need
to be checked.
If the checks above are OK:
If you have a low pressure accurate pressure source you can hook it to
the regulator and check it at 0-5psi and note the fuel pressure rises.
If you don't have a low pressure source then...
Start the engine and run it up and monitor the fuel pressure which is
not hooked up as a differential fuel pressure (if you have a
differential gauge it is still hooked up as above). Note as the airbox
pressure builds how the fuel pressure behaves. As the boost increases
the fuel pressure should go up about one to one. So when you see 2 psi
airbox pressure at about 34 inches MP the fuel pressure should be 6. At
full boost the fuel pressure is about 10, the airbox is about 5 psi
boost and the MP is at 40 inches. If the pressure is not rising, then
the pressure regulator has quit.
In flight symptoms of a fuel pressure regulator failure is the engine
will run fine below 30 inches on the ground, but will lean out and begin
to either loose power or cut out depending on how severe the pressure
regulator failure is. You will normally only be able to run at low
altitude and the engine does not run well above 26 inches and the
throttle will be severly reduced.
Your solenoid is easy to check on the ground by hooking up a bit of
vacuum or very slight pressure and checking the line from the starboard
airbox pressure inlet to the solenoid. Between 100% to 115%, push the
throttle up with the engine off and electrical power to the TCU and move
the throttle and observe that the solenoid opens above about 108%. Oh
by the way, this little 90 degree pressure tap sometimes gets clogged
with oil from the turbo and should be clean. When you disconnect the
line, squirt a blast of carb cleaner in the tap and make sure it is
clean.
If you just rebuilt your carbs, be sure to check you didn't
inadvertently install your Bing compensating pistons 90 degrees out.
Duh, I've seen it done when carbs are rebuilt. All it takes is on
assembly, is to put a slight turn on the needle during reassembly. Only
the rubber gasket in the top keeps those pistons in position and there
is a slot where the rubber goes in to hold the carb pistons from
rotating. I have seen the chokes installed incorrectly which leans out
the engine also.
The Rotax troubleshooting guide is nice but assumes the engine is brand
new and your airplane hookup is poorly done. Nothing on an older engine
with problems is presented, nothing to help those of us with problems
after a carb rebuild, or how to track a defective part like a bad
gasket. Just take it apart and rebuild it or buy two new carbs seems to
be the factory answer.
Go off and test that fuel system, check your TCU servo moves the
wastegate OK and you don't have any airbox leaks... Back to the carbs to
just check the rebuild you did for simple things and in your case, make
sure the float bowls are dead dry. Any wetness, you need to put in new
gaskets.
I just received cork gaskets from Bing Carbs and will put them in mine
to test, as paper gaskets are supposed to be used on the 914. I am
serious about sealing my carb gaskets if this does not work and may even
put a non rubber O ring gasket (most likely thin paper with the original
phenolic) back on the bottom.
I have always felt that if it isn't broke, don't fix it. Two very
experienced Rotax repairmen I trust, swear by rebuilding the carbs every
200 hours or if they have been sitting a while, as they are a ticking
time bomb. I now see they are right about the carbs and we do follow
these guidelines religiously. Since the service manual says to rebuild
the carbs at 200 hours I now choose to rebuild if I am within 50 hours
of 200 hours or the carbs have been sitting 6 months due to extended
down time... Ed and I can rebuild the carbs in about an hour, and
rebalance the carbs in less than 1/2 hour. The delay is in the soaking
and cleaning of the carbs once disassembled, and the soaking of the
paper gaskets. I hope the cork fixes the paper gasket problems, (or the
rubber gaskets I've heard of work out), and improves the time between
carb overhauls.
Just my procedures, I welcome other inputs for sure. We are all
exhausted down here with it on Rotax and Jabiru with Bing carbs. I
don't care if the engine was running great when it came in, if it meets
the criteria above, the carbs get rebuilt.
Regards,
Bud Yerly
Europa Tech Support
Custom Flight Creations, Inc.
www.customflightcreations.com<http://www.customflightcreations.com/>
(813) 653-4989
----- Original Message -----
From: ploucandco<mailto:ploucandco@YAHOO.COM>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Sunday, June 10, 2012 11:31 AM
Subject: Europa-List: RPM drop with a 914 above 100%
<ploucandco@yahoo.com<mailto:ploucandco@yahoo.com>>
Hello all,
Recently, I had to about a Take off with my Europa 914 airmaster due
to the fact that I was facing an RPM drop above 100%. The ROTAX has less
than 330 hours.
I already looked at the following items:
- replaced the fuel with fresh one
- fuel pressure is OK
- TCU - transfer function according to heavy maintenance manual and
solenoid gets 12V above 108%, so should be OK
- turbo wastegate fully closes
- air filter cleaned up
The issue is still and my next step is to look at the carbs (membranes
have been replaced less than 200 hours ago). Any other ideas? Where
should I specifically need to look at the carbs?
The attached file from the TCU log depicts the issue starting from
line 989.
Thanks for relevant input.
Jacques
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