Question for 912 operators.....

GyrOZprey

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On a couple of occasions in the last month ... my 912 has had a very fleeting momentary power-drop on TO @ WOT! ( So brief in fact I was asking myself ... was it real ... or imaginary???? :confused: )

The first couple of times it happened ... it was so quick & fleeting ... then everything ran absolutely normally ... I thought it was just me - being neurotically hypersensitive ... & thinking ... did it REALLY happen .... well yesterday ... there was no ? ... it was definitely a very quick & real momentary drop in power at WOT on take-off ..... and seemed to reoccur as I flew the length of the runway playing with the top end of the throttle setting ... trying to get it to repeat .... just a little burp / hesitation in the power!

Max E rpm ... showing on my MGL instrument is only 5400 .... due to my prop pitch ( then @ 11.5 - @ tip) ... which I have now taken back to 10.3 (@ the tip) - about 13.5 at the 75% point .... & will see if I get my former climb performance & E rpm of 5600 back!

IDEAS ????? .....Fuel contamination ... particles / water from the high humidity!


First I'm going to install the gascolator project I've been planning for a while ( since switching to airport Mogas (from the ethanol stuff from the gas station - treated with Seafoam)

I currently have two of the round see-through mesh-screen rotax fuel filters in the fuel line ... ahead of both fuel pumps! I have never seen any particles / crud on the screens ... but they are a coarser mesh than in the gascolator.

I remember Birdy once had some crazy intermittent power drops in his machine ... turned out to be a bit of junk blocking a jet on & off! ( I'm NOT wild to tear into the carbs & have to do a carb balance again) .... until eliminating everything else!

Until I get the gascolator installed I've been draining my tanks & putting my fuel through Mr Funnel before refilling ... when the gyro has sat for a couple of weeks due to the extreme humidity we had this year!

Any suggestions?????
 

All_In

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Hi Chris,

It does sound like water if it only happens once per flight and shortly after take-off when you change your angle of attach and the water flows through.
 

JEFF TIPTON

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You might consider moving one of the fuel filters between the mechanical filter and the carburetors. This trap any contamination for the mechanical pump.

As to the problem, remove the carburetor bowls and check for any contamination. If nothing is found here, then I would go back to the fuel that you were using. Did that make a difference. If it does then we are looking at two possibilities. The fuel from the gas station would likely not have water showing in the fuel as the alcohol would have the water in suspension. On the other hand, the airport mogas, how old is it. Not saying it is bad but, if it is a winter blend fuel that is in his tanks then the fuel may be vapor locking. Under the right conditions even the current blended fuel could have a vapor lock. Fuel systems that are pressurized are effected the least.

By the way if you gyro has a fuel pressure gauge did you notice it being any different. Higher or lower.
 

Jason O

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I had trouble with a 912S at high power settings. I took a look in the float bowls and found a couple of drops of water. They just roll around on the bottom of the bowls like beads. My theory is that at high fuel flows they get sucked up and at low flows they just sit on the bottom of the bowl.
 

All_In

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You might consider moving one of the fuel filters between the mechanical filter and the carburetors. This trap any contamination for the mechanical pump.

As to the problem, remove the carburetor bowls and check for any contamination. If nothing is found here, then I would go back to the fuel that you were using. Did that make a difference. If it does then we are looking at two possibilities. The fuel from the gas station would likely not have water showing in the fuel as the alcohol would have the water in suspension. On the other hand, the airport mogas, how old is it. Not saying it is bad but, if it is a winter blend fuel that is in his tanks then the fuel may be vapor locking. Under the right conditions even the current blended fuel could have a vapor lock. Fuel systems that are pressurized are effected the least.

By the way if you gyro has a fuel pressure gauge did you notice it being any different. Higher or lower.
Oh that's right it mogas. I was thinking 100LL.
 

Ronin

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I had trouble with a 912S at high power settings. I took a look in the float bowls and found a couple of drops of water. They just roll around on the bottom of the bowls like beads. My theory is that at high fuel flows they get sucked up and at low flows they just sit on the bottom of the bowl.
I second that, happened all too many times to me.
That and change the filters.

Jim
 

Smack

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easy

easy

It's easy to drop the 912 float bowl for a quick check.
At the same time, you can examine the jets (wire? carb cleaner?) easily without taking the throttle cable off (MY installation, anyway) and thus avoid a carb re-sync (which isn't too difficult anyway).
Brian
 

birdy

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I remember Birdy once had some crazy intermittent power drops in his machine ... turned out to be a bit of junk blocking a jet on & off! ( I'm NOT wild to tear into the carbs & have to do a carb balance again) .... until eliminating everything else
Not exactly how mine reacted, but could be sumthn as simple asa drop of water in the bowl.
Usualy, at WOT, a few beads of water will just pass through the jet with no harm.
If theres alot of water, youll loose rpm and suction and it wont pass it, you have to drop the bowl.
Mine was a flake of brass/ copper lookn stuff that was sitn rite under the jet.
WOT sucked it up and blocked the jet till i backed off n it droped back into the sump of the bowl.

Simply slip the bowl clip forward and drop the bowl off, checkn for anythn on the bottom.
Just be sure you get the bowl up snug n square before you slip the clip back under it.

Pice o cake.;)
 

GyrOZprey

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Thanks all for the suggestions :hail: ... off in the morning to work on it!

Drop carb bowls ( familiar with this process! :) ) ... look for water drops, install gascolator ... move the filter that will be replaced by gascolator to post mechanical pump position & try some of the gas station fuel!
 

Cammie Patch

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How many hours and years on the carbs since new or overhaul?
The 200 hour overhaul is very important. It will thoroughly clean any contamination and varnish. The kits come with all the o-rings, needles and jets that you will need. If you have more than five years on your carb sockets you want to get those too. The rubber parts wear out over time such as years, and the metal parts like the needles will wear with hours on the engine. I have overhauled eight Bing carburetors in the past few months, and it is one of the best things you can do for your engine if it needs it.
Rotax owner.com has a great video on how to do the overhaul.
 

GyrOZprey

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Good point Cammie!

Good point Cammie!

How many hours and years on the carbs since new or overhaul?
The 200 hour overhaul is very important. It will thoroughly clean any contamination and varnish. The kits come with all the o-rings, needles and jets that you will need. If you have more than five years on your carb sockets you want to get those too. The rubber parts wear out over time such as years, and the metal parts like the needles will wear with hours on the engine. I have overhauled eight Bing carburetors in the past few months, and it is one of the best things you can do for your engine if it needs it.
Rotax owner.com has a great video on how to do the overhaul.

Hours since overhaul .... about 66 ! ....
I installed a used 912 ( - a 2006 model ... about 327 TT since new when I got it!)- on my new gyro frame ..... spring 2012 !

At Hobbs ~ 20hrs... During summer of 2012 a local rotax trained mechanic & I did compression & trickle down tests ... replaced O rings where coolant was leaking around the cylinder heads ..... both carbs got full service with new stuff from the kits I bought ...even though they had evidently been done not too long before I got the engine ... & I thoroughly cleaned all the varnish & gunk out!! ( I really got to know my engine quite well working with the LSA mechanic & then in January 2013 went to Rotax school @ Lockwood getting the service & repair training for myself)
The carb sockets were new also & in great shape!
After seeing the dried fuel gunk when I cleaned them ... if the gyro is going to sit for a few weeks ( in winter) ... without running I have been emptying out the bowls ... at least!

Hobbs now is @ 86!

I found the problem today ... causing the power drop @ WOT .... one carb bowl had a big black flake ... of something floating around on the bottom!!! .... seems a bit like Birdy's scenario ... sucked up to block the jet @ WOT & fall back when I backed off throttle!

It's good to find a definite cause for the problem!:rolleyes:

I got the gascolator mounted & plumbed in ... drained & fresh gas in the seat-tank, carb bowls dumped .... did a test runway fly-over just before sunset ... when the winds dropped .... it seems to be running great now! :whoo:
 

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All_In

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So glad you found it... way to go!!!
 

Zooom909

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Sounds like you found an Obama dropping in your carb bowl... Not surprising with
All the Obama droppings everywhere...
See you in Mentone..
 

GyrOZprey

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Weird side lighting .....

Weird side lighting .....

Looks like the black flake could have come off the float itself

Glad you found the problem.
... when I took the photo...made it look like the float material was disintegrating or there was gunk attached to / flaking off the float tops! :eek:

When I studied the picture on a large computer screen ... I was astounded that I had apparently missed seeing anything amiss with the floats ... maybe I was SO focused on the black particle ... I really didn't notice the state of the floats! :confused:

Just to be sure - today I dropped the bowl again & dried off each float & looked them over - hard - out in the full sunlight! Smooth ... perfect condition ... NO crumbly gunk .... as seems to be showing in the above picture!

Most strange optical illusion! :noidea:
 

All_In

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... when I took the photo...made it look like the float material was disintegrating or there was gunk attached to / flaking off the float tops! :eek:

When I studied the picture on a large computer screen ... I was astounded that I had apparently missed seeing anything amiss with the floats ... maybe I was SO focused on the black particle ... I really didn't notice the state of the floats! :confused:

Just to be sure - today I dropped the bowl again & dried off each float & looked them over - hard - out in the full sunlight! Smooth ... perfect condition ... NO crumbly gunk .... as seems to be showing in the above picture!

Most strange optical illusion! :noidea:
That's good to learn!!! It did look like float material/ = denigrating??
 

themonarch

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Gremlins

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Hi Chris,

Of course I have followed your post concerning your engine's problem with what looks to have been a contaminant inside of the carbureator.
So glad to read that you were able to isolate the cause before something unfortunate could happen.
I am presuming that you may have been helped along by the various contributors who responded.
Assistance and suggestions from those "who have been there" is precisely what a forum such as this is for. This heartens me. My respect to all who bothered to help. From time to time we all can use some. MJD
 

birdy

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Just a SCG tip, wen ever you do ANYTHN in the fuel systm, chech filter flow rates, change filters, or anythn that opens the systm, take the bowls off, run the electric pump ( every machine should have a duplicat fuel pump) and flush the systm while the float needles are full open. While the pump is still runing, and you recon any contaminants have flushed through, hold each float up gently to the level position and be sure the both close 100%, at the same time (to be sure the needles seal at opperateing pressure)
 

Sky Scooter

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Obama Droppings,

Obama Droppings,

Hey Chris good you found it, I was just wondering if you have had any fuel line issues that black stuff could be telling you some thing more.I had to change mine at low hrs as they were cracking, cheap stuff used during build. There are two ratings for this tube 07 and 09. The 09 stuff is expensive but bullet proof, as it takes a few hours to replace the fuel lines it's worth it as you won't have to revisit it for a while. The high octane fuels we use these days i believe is the culprit as it seems to eat rubber. I'm using BP Ultimate and i know i'll need to replace my fuel tank inspection nipples soon too. Anyway just keep an eye on it mate that black stuff might have come out of your fuel line. Might be worth looking at it from the inside.

Mike.
 
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