Guys, Here is my one and a half cents.
When working with Jerry Hope's 914 we found that the reset switch was
all that was necessary to cure the surging... That is always my first
in-flight correction. For my older engine, the wiper on the pot in the
turbo servo wore out with time and the servo began to hunt. By hitting
the reset switch, it momentarily cuts the power and stabilizes the
manifold/boost and the servo related surge/boost fluctuations stop.
As for the carb related problems, With the engine at idle, servo locked
out (reset switch held to eliminate the servo from operating), run the
engine up until you see about 35-39 inches of MP. If the engine does
not surge, it is not the carbs. If you have the dual manometers, and
can watch the MP on each carb, that will tell you volumes about your
carb health. If one of the altitude compensators is hanging up, the
engine will sag, calling for more boost, then the engine boost clears
the carb balance problem, but that causes a momentary over boost which
then causes the servo to cut boost, which then causes the carbs to be
out of balance again. In this case you will see it in the twin
manometers and a carb rebuild kit for $45 will fix you up. The carbs on
a 914 take about 2 hours to get on and off, and 1 hour to replace the
seals in the carbs. Then you get to retune the throttles. Pay
attention to the position of the needle valve slide clip during the
rebuild. If you get one position off, you will be running richer or
leaner than normal. Bing has troubleshooting manual on the web and
Rotax has the carb balancing video you can order, so check it out.
If your throttle position sensor is worn, that too can cause the
computer to force the engine into a surge on the older slower computer
processor. The program sold by Rotax can check the position sensor.
For low boost, or leaks, wow, that's a new one on me. I don't get to
fly that high so I have no experience. My low boost problems is because
I don't set the cable right on the servo or the cable slips.
Rich Schultz found with running on AV Gas, his carbs stayed in tune if
he added just a bit of Marvel Mystery Oil to his gas to lube his carb.
His problems cleared up.
Bud
Custom Flight Creations
(813) 653-4989
----- Original Message -----
From: Paul McAllister<mailto:paul.the.aviator@gmail.com>
To: europa-list@matronics.com<mailto:europa-list@matronics.com>
Sent: Thursday, October 09, 2008 9:20 PM
Subject: Re: Europa-List: engine surging
<paul.the.aviator@gmail.com<mailto:paul.the.aviator@gmail.com>>
Hi Folks,
Could I offer a contrary view? I got to 600 hours on my 914 with no
sign off issues wih the carbs, but on the adivce of many I sent my
carbs into Lockwood to have them overhauled. What a mistake, the
airplane now uses .3 to .4 more gallons per hour than before and it
took me 4 tries to get the inlet system sealed up again so I could get
maximum boost.
Actually it still is not right, I can only get 27 inches and 16k feet
and I should be able to get 34" so the darn thong is still leaking.
With that said, it may well be your carbs, but the first place I would
go is fuel filters, then look at the fuel pressure (needs to be
measured differentially), then onto the turbo waste gate. What you
will need to do is disconnect the cable and move it by hand to check
for "stickyness".
After all of the above, yep, I'd mess with the carbs.
Just my 2 cents worth.
Regards, Paul
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