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Power loss

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Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Tue Jul 28, 2009 6:09 pm Post subject: Power loss

Had some engine trouble today which has me scratching my head...



Cuyuna ULII-02, Mikuni carb, airport near sea level, 80°F and humid (don't 

know the actual RH).  Had a 300 main jet, EGT maxed out around 1100, 

wouldn't hold rpm at 5500 cruise without playing the throttle, and 

hesitation when advancing the throttle from cruise.  After flying today, I 

switched to a 290 main jet.  EGT went up a bit, maybe 1150.  Flew around 

for awhile, around cloud level (2000') at low cruise (4500 rpm).  Rpm's 

wouldn't go up when I opened the throttle, then they dropped further to 

idle, regardless of the throttle position.  I thought perhaps the throttle 

cable had broken, but it hadn't.  Didn't think to check the fuel pressure 

gauge.  A shot of prime did nothing.  After a while (as I was, of course, 

gliding back to the airport) the rpm's picked up, first to around 4000, 

then back to normal.



By the time I was down it was as if there was no problem.  Plugs looked OK, 

perhaps a bit on the lean side but not by much.  At any rate, I put the 300 

jet back in and dropped the needle from the middle to the second clip 

notch.  This put WOT at 1100 EGT again, and high cruise around 1150, with 

no hesitation when the throttle was advanced.  After some ground running, I 

took off again and had no trouble.



I'm still not clear on what's going on.  Not a lean seizure if it kept 

running at idle for a minute or two.  Fuel delivery problem?  No evidence 

of that but the fuel level in the tanks was somewhat low (I filled before 

flying again).  Carb ice?  The conditions were certainly right and the 

outside of the intake manifold was wet, but that's normal and these engines 

aren't that susceptible to carb ice.  At this point I just don't know.



-Dana

--

  Politicians are those who deal with the problems which would not exist if 

they didn't exist.

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mdnanwelch7(at)hotmail.co
Guest

Posted: Wed Jul 29, 2009 3:08 am Post subject: Power loss

 Dana C

  

     I have experienced similar situations you described twice (not being able to get full throttle).

 Although I can't say if every one of my "symptoms" were identical to yours.

   It seems safe to initially assume you have a fuel problem.  Both of my examples were fuel related. 

  

 They were;

   A) accidently cocked open the fuel strainer petcock on pre-flight inspection C allowing air to suck in at higher power setttings C reducing rpm to idle (at climb-out!!)

   B)  a little chunk of debris in the fuel tank that would occationally plug the exit hole C reducing rpm to idle (at climb-out C too!!)

  

   If I had these occur again C I'd check for air leakage in "A" by spraying carb cleaner lightly around the entire fuel system C listening for any rpm increase.

  

   Next C I would thoroughly clean EVERY inch of the fuel system C to include complete disassembly if necessary.  From the tank to the pistons C I'd make sure it was spotless.

   When I'm faced with cleaning a carburetor that I suspect is contaminated C I clean it over a pristine cloth (after scrubbing the outside C first!).  That way C if any crap lands on it C I know it came from inside the carb.  For me C I like to know if I may have found the culprit.

  

 Best of luck C 

 Mike Welch

  

  

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed Jul 29, 2009 4:48 am Post subject: Re: Power loss

Dana,



Carb ice is one of those things that is difficult to prove was the cause but your description of the problem makes me believe that is a high probability, even on these carbs. The fact that it seems to have been transient contributes to that guess. 



BUT Mike is right to recommend a thorough inspection of the entire fuel delivery system. If nothing abnormal is found, then that too adds to the probability of carb ice being the cause.



Fuel delivery problems kill a lot of aviators. Be as sure as you can before you fly again.

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Thom Riddle
Buffalo, NY (9G0)

Don't worry about old age... it doesn't last very long.
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williamtsullivan(at)att.n
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Posted: Wed Jul 29, 2009 5:42 am Post subject: Power loss

Dana- I don't know much about aircraft carbs, but I have had two older trucks that had occassional carb ice.  One was a 1980 Chevy van, with a straight six.  The manifold heat tube arrangement had rotted off, and it would ice up and go to just about an idle.  After sitting by the side of the road for a few minutes, idling, it would melt the ice and return to normal.  Cardboard over the radiator solved it.  The outside of the carb was wet with condensation.  Same thing with a 1951 Dodge M-37.  It would head for an idle, and sometimes pulling the choke out for a second would cause it to swallow the ice.  Wet carb exterior again. Cardboard, again. The Dodge would also get vapor locked on a hot day.  Poured cold water on the fuel pump, and it would run.  No exterior moisture when vapor  locked.

   Considering our weather lately (Dana is 30 miles south of me, in the same river valley), it sounds like carb ice.  Very humid for quite a while, now.  I don't know about the Mikuni, but a Bing doesn't have a true choke- no way to manually increase carb vacuum and shake out the ice like was possible with the Dodge.  I can't think of a way to duplicate the conditions on the ground- maybe somebody else can.  Good luck, and be careful.

  

                                             Bill Sullivan

                                             Windsor Locks, Ct.

                                             FS 447

 Hot, overcast, and very humid again.

 [quote][b]

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by0ung(at)brigham.net
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Posted: Wed Jul 29, 2009 10:18 am Post subject: Power loss

After a while (as I was, of course, 

gliding back to the airport) the rpm's picked up, first to around 4000, 

then back to normal.



 	  Quote: 	
		  >>>>>>>>>>>>>>>>>>>>>.


	


80 deg on the ground...  at 2000 ft the air temp should have been around 70

or so.   That is kind of the high side for carb ice,,,,   when lowering back

to ground level the temp would go back to 80 and that should have been warm

enough to melt the ice out.  This may be an explanation of why the rpm came

back.



Boyd Young

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Thom Riddle

Joined: 10 Jan 2006
Posts: 1597
Location: Buffalo, NY, USA (9G0)

Posted: Wed Jul 29, 2009 10:43 am Post subject: Re: Power loss

Carb ice is actually quite possible in high humidity conditions at 80F. See attached jpg image of a carb icing chart.

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Thom Riddle
Buffalo, NY (9G0)

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Dana

Joined: 13 Dec 2007
Posts: 1047
Location: Connecticut, USA

Posted: Wed Jul 29, 2009 2:25 pm Post subject: Power loss

It _does_ sound like carb icing.  I hesitate to say that because I chased 

carb ice on one other hot humid day and the problem turned out to be 

jetting related, and carb ice is nearly impossible to prove... but 

conditions were certainly right... 80F on the ground, chilly and 99.9% RH 

at 2000' where I was flying at low cruise power.  I now think the jet 

change I did right before had nothing to do with it, just a coincidence.



I don't think my fuel system was the culprit as it's in good shape, with 

two separate tanks feeding the first stage fuel strainer, which has a large 

outlet screen (nearly impossible to plug) feeding the line to the main 

filter... and clear fuel line and filter (sorry John H.) so I can see any 

bubbles.  I really wish I'd thought to look at the fuel pressure gauge when 

it was happening.



-Dana

--

  He's dead, Jim.  Grab his tricorder and his wallet.

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aslsa.rng(at)gmail.com
Guest

Posted: Wed Jul 29, 2009 7:39 pm Post subject: Power loss

Dana, If you know someone who has a copy of the Rotax Heavy Maintenance Manual for the 462-532-582 series engines you might want to check out chapter 10. It discusses a series of things to check for just the symptoms your engine exhibits.  The chapter originally appeared as an article written by Nigel Beale of Cyclone Hovercraft of England. Pat may know of him and be able to tell you where a copy of the article can be found on the web.

 Rick Girard

do not archive



On Wed, Jul 29, 2009 at 5:17 PM, Dana Hague <d-m-hague(at)comcast.net (d-m-hague(at)comcast.net)> wrote:

[quote] --> Kolb-List message posted by: Dana Hague <d-m-hague(at)comcast.net (d-m-hague(at)comcast.net)>

 

 It _does_ sound like carb icing.  I hesitate to say that because I chased carb ice on one other hot humid day and the problem turned out to be jetting related, and carb ice is nearly impossible to prove... but conditions were certainly right... 80F on the ground, chilly and 99.9% RH at 2000' where I was flying at low cruise power.  I now think the jet change I did right before had nothing to do with it, just a coincidence.

  

 I don't think my fuel system was the culprit as it's in good shape, with two separate tanks feeding the first stage fuel strainer, which has a large outlet screen (nearly impossible to plug) feeding the line to the main filter... and clear fuel line and filter (sorry John H.) so I can see any bubbles.  I really wish I'd thought to look at the fuel pressure gauge when it was happening.

  

 -Dana

 --

  He's dead, Jim.  Grab his tricorder and his wallet.

 

 

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pj.ladd(at)btinternet.com
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Posted: Sat Aug 01, 2009 7:17 am Post subject: Power loss

Nigel Beale of Cyclone Hovercraft of England.  Pat may know of him >.

  

 Hi,

 Pat certainly knows of him. He is THE MAN in the UK  on all things Rotax.

  

 Cheers

  

 Pat

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