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RPM drop with a 914 above 100%

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ploucandco

Joined: 16 Sep 2007
Posts: 69

Posted: Sun Jun 10, 2012 7:31 am Post subject: RPM drop with a 914 above 100%

Hello all,



Recently, I had to abort 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 present 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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budyerly(at)msn.com
Guest

Posted: Sun Jun 10, 2012 6:25 pm Post subject: RPM drop with a 914 above 100%

<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]-->  Jaques,

 I had to remove the 914 manual from this attachment.

 You probably already downloaded the 914 repair manual.

 Regards,

 Bud

 ---

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rlborger(at)mac.com
Guest

Posted: Sun Jun 10, 2012 6:48 pm Post subject: RPM drop with a 914 above 100%

Bud,



I don't think you received my commentary on the nitrile gaskets.  From a previous e-mailing:

FWIW, the nitrile gaskets are probably OK if you have the carb off and are doing a rebuild.  Where you can turn the carb upside down to put the gasket in place and properly fit the bowl to the carb body without disturbing the gasket.  Otherwise they are too floppy to try and install on the bottom in an upright carb, in amongst the exhaust manifold and various plumbing on the aircraft.  I was very careful, checked them with a mirror for location and fit, still they moved out of position while getting the bowls back on and tight.  Ended up with both gaskets cut by the bowl.

Also, my float bowl nut uses an O-ring and not a flat gasket.  The torque is 4 ft-lbs.



 Blue skies & tailwinds,

Bob Borger

Europa XS Tri, Rotax 914, Airmaster C/S Prop.

Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP

3705 Lynchburg Dr.

Corinth, TX  76208-5331

Cel: 817-992-1117

rlborger(at)mac.com (rlborger(at)mac.com)

 

 

On Jun 10, 2012, at 9:23 PM, Bud Yerly wrote:

…< Snip >...

 

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.

 

…< Big Snip >...

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