Engine trouble on takoff

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Warmi
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Engine trouble on takoff

Post by Warmi »

Had my first real scare ….

My engine was running a bit rougher than I remember for a last month or so - I couldn't quite place my finger on it , it was running fine just occasional odd pulsing like vibration here and there and once, what I thought my power rolled back during cruise to about 4500 – when I advanced the throttle it went back to 5100 almost instantly – I wasn't sure if it was the engine or I bumped the throttle or what - I thought I was getting paranoid

Well, then one day … when I was taking off , the plane was just about to rotate with full power when it suddenly dropped to about 4500 or so - no real vibration or anything, just as if I pulled the throttle back – and then it wouldn’t come back , when I went back to the hangar all I could get is about 4500 at full power.

Turned out to be a piece of debris in one of the carbs – it was basically a chipped off piece of the float, I could actually see the corner that was sliced off and the piece was sitting in the bow.

I don’t know how could that happen – last time the carbs were opened was during the annual a few months back – is it possible that someone was a bit careless and sheared off the corner when putting the carbs back together ?
After cleaning the bowl and inspecting both carbs – I went around the pattern twice and the engine was smooth as ever – but I am still wondering how this float got mangled in the first place ?

I record all my flights so here is the actual video of this happening with some pictures of the offending debris …

https://youtu.be/PCmdNnOrXOc
Flying Sting S4 ( N184WA ) out of Illinois
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ShawnM
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Re: Engine trouble on takoff

Post by ShawnM »

Did they look like this? Peeling floats was an issue with one batch of floats and I had mine peel also. There's a notice from Rotax about this. Thankfully Rotax and Lockwood gave me a new set for free. I inspect my floats quarterly now until I know this isn't an issue anymore. I now have the latest generation of carb floats and so far so good. I never had any issues with it running rough as I caught it before any clogs happened.
861182 float separation pic (Medium).jpg
861182 float separation pic (Medium).jpg (82.67 KiB) Viewed 7935 times
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Warmi
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Re: Engine trouble on takoff

Post by Warmi »

Nope, it actually looked like somebody literally sliced off the corner - a reasonably clean cut - it matches with the metal part part of the carb the bowl goes over - that's why I am thinking it is a mechanical damage and not floats peeling off.

These floats are the original floats from 2012 - I am thinking if they were a bad batch that was going to go bad I think by now I would know :-)
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Re: Engine trouble on takoff

Post by drseti »

Any floats that date back to 2012 should certainly have been replaced by now - this is a known issue, about which Rotax has put out several different service bulletins over the years. I'd strongly recommend you replace all four floats ASAP - they cost $100 a pair. And I weigh floats individually at every 100 hour inspection - typical weight of good floats is about 2.8 grams.
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Re: Engine trouble on takoff

Post by Warmi »

drseti wrote:Any floats that date back to 2012 should certainly have been replaced by now - this is a known issue, about which Rotax has put out several different service bulletins over the years. I'd strongly recommend you replace all four floats ASAP - they cost $100 a pair. And I weigh floats individually at every 100 hour inspection - typical weight of good floats is about 2.8 grams.
They weight about 6 grams , the set - so I am still well under the limit - I will order them and replace but I see nothing wrong with them except that one chipped corner so I am still wondering what happened , and if it was maintenance induced issue.
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Re: Engine trouble on takoff

Post by drseti »

It's true that the service bulletin calls for under 7 grams per pair (I think), so your 6 grams meets the soec. I still prefer to weigh them individually, and match pairs so they push up symmetrically on the fuel flow metering mechanism. Thus, the 2.7 grams each that I typically see.

With a corner sliced off one float, I see two possible concerns. You may have asymmetry with the other float (the sliced one will actually be a tad light, although the service bulletin doesn't actually address this). And, there's a possibility that, with the missing protective outer surface, the exposed foam core with will absorb fuel over time, leading to a heavy (sinking) float, which will let the float bowl overfill and flood the carb.
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Re: Engine trouble on takoff

Post by Warmi »

Another question - I still have the cork gasket in both of my carbs.

Since I am gonna be replacing floats may as well replace the gasket - Is the fiber one preferable or does it even make any difference ?

I had my 200 hours inspection done ( at the same time with my 5 year rubber replacement ) and carbs were deemed in good condition and I don’t see a single carb related item on the replacement bill I got during that service - I am still confused a bit , does 200 hour inspection require carb overhaul or just inspection and if the carbs are deemed good then nothing special should be done ( as it was in my case ) ?

PS.
Actually correction ...

They replaced the the diaphragm:
861 116 - Diaphragm
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Re: Engine trouble on takoff

Post by drseti »

Yes, the diaphragms and carb sockets are part of the 5 year rubber. 200 hour carb inspection is just that, unless problems are found (in which case, an overhaul is in order). And every time I pull the float bowls, I take a close look at the gaskets. If they're in good shape and no leakage, I don't replace them. But when it does come time to replace them (or any time I do a carb overhaul), I certainly don't use cork.
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Re: Engine trouble on takoff

Post by Warmi »

Alright , sounds good - gonna order the parts and swap the floats - thanks for you help guys.
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Re: Engine trouble on takoff

Post by FastEddieB »

I had an issue when I used a thin layer of silicone gasket sealer to hold the float bowl gaskets in place. DON'T DO THAT!!!

The silicone can react with the gas and turn to jelly:

Image

Pretty sure this is what caused some very rough running over wooded terrain in S GA, leading to me declaring an emergency. Fortunately it smoothed out in a minute or so and all was well.

I learned that just a touch of grease is the ticket to hold the gaskets in place. When gas hits grease, it just harmlessly dissolves.

Lesson learned!
Last edited by FastEddieB on Sun Jun 02, 2019 3:02 pm, edited 1 time in total.
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Re: Engine trouble on takoff

Post by MrMorden »

Get the green fiber gaskets when you order your floats. They are pretty cheap, and cork is notorious for flaking off and causing bowl.leaks or putting debris in the bowl.

Before putting the new gaskets in, soak them overnight in gasoline. This will cause them to swell slightly and make a better seal -- that is what Lockwood told me, and it works. You can also smear the gasket with white lithium grease, that helps some as well. I do both and the combo cured persistent minor leak issues.
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Re: Engine trouble on takoff

Post by Wm.Ince »

MrMorden wrote:Get the green fiber gaskets when you order your floats. They are pretty cheap, and cork is notorious for flaking off and causing bowl.leaks or putting debris in the bowl.
Before putting the new gaskets in, soak them overnight in gasoline. This will cause them to swell slightly and make a better seal -- that is what Lockwood told me, and it works. You can also smear the gasket with white lithium grease, that helps some as well. I do both and the combo cured persistent minor leak issues.
Great advice, Andy! :D
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Re: Engine trouble on takoff

Post by 3Dreaming »

Get rid of the cork gasket! Actually they don't sell the fiber gasket anymore. The new gasket is a rubber type material. They changed sometime last year.
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Re: Engine trouble on takoff

Post by MrMorden »

3Dreaming wrote:Get rid of the cork gasket! Actually they don't sell the fiber gasket anymore. The new gasket is a rubber type material. They changed sometime last year.
Interesting....I guess I need to change mine too!
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Re: Engine trouble on takoff

Post by Wm.Ince »

MrMorden wrote:
3Dreaming wrote:Get rid of the cork gasket! Actually they don't sell the fiber gasket anymore. The new gasket is a rubber type material. They changed sometime last year.
Interesting....I guess I need to change mine too!
Me too!
Bill Ince
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Retired Heavy Equipment Operator
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