912 S powering off on Bouncing landings

by Dan Liles in 912 / 914 Technical Questions 13 years ago

I have a Kolb Mark 3 Xtra with a 912S. I have only flown this setup for about 20 hours. I have been landing on a grass strip at my local airport untill recently. I have been venturing out to friends private strips. Some of the strips are a little bumpy. I have had situations where the engine will completly power off on a hard bounce. I have checked all of the grounds and other wiring. Everything seems secure. The engine is a 2001 model but has only been in service since 2007 and has a total of 94 hours. Has anyone experienced this? Or does anyone have a recomendation of what to look for?

Thanks,
Dan Liles

Re: 912 S powering off on Bouncing landings

by Roger Lee » 13 years ago

Roger Lee

126 5.14k 4.58k

Hi Dan,

Two things come to mind. Yes it could be a wire if it shuts off immediately like you turned off the key at little bumps or just one bump. That would be electrical. If you have to bump and bounce around a little and it just dies like running out of fuel then I'm going for the problem listed below.

I used to own one of the first Kolb Mark III's in the country to have a 912ULS. Great little plane, it went every where.
Here is most likely your problem. If you land on a bumpy field and depending on how many bumps you encounter in a row, you are sloshing the fuel and floats in the carbs. This causes them to vent some fuel out the vent tubes most likely and they can not control the fuel in or out of the carb bowl bouncing all over in the bowl. Like you said it doesn't happen on smoother runways. This plays havoc with the float needle and float level.

p.s.

When you check ground connections of any fitting they are loose until you put a wrench on them.
Something may be finger tight, but wrench loose. This has helped me find so many problems I can't even count.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: Dan Liles

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Re: 912 S powering off on Bouncing landings

by Dan Liles » 13 years ago

Dan Liles

2 1 0

It is shutting down after a series of bumps not after a single bump. Did you ever experience this with yours? If it is the problem dou you know of a fix? The concern I have is if I ever needed to power back up quickly for a pass.

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Re: 912 S powering off on Bouncing landings

by Roger Lee » 13 years ago

Roger Lee

126 5.14k 4.58k

Hi Dan,

I do not know of a fix. You could try some different tires and tire pressures to help cushion the bumps. There is no way to keep the floats from bouncing. I hate to say it, but if the tire tip doesn't work then help the guys smooth the field.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: 912 S powering off on Bouncing landings

by bill martin » 13 years ago

bill martin

10 757 0

Sounds like roger is on the right track Dan. Sloshing in the carb bowl would have to be pretty bad and you would get a lot of sputtering and coughing before it actually shut down. A ground in the mag switch circuit could cause a shutdown. In fact, thats about the only circuit I can think of that could kill the engine if it went to ground. If you have a mag switch that has right, left, and both all in the same switch, That may be a place to start looking. It's the only place I can think of where both mag kill circuits come together in one switch.

Hope this helps,

Bill

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912 S powering off on Bouncing landings

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