Throttle Cable Break

by Jospeh Kiefer in 912 / 914 Technical Questions 14 years ago

The throttle cable to the right carb on my Sport Cruiser's 912ULS is starting to break (two strands gone)at the point it attaches to the throttle arm. I've ordered a replacement but the experiance got me to thinking about what we should do if a throttle cable did break. The spring on that carb would take it to full throttle which would give you a very unbalance engine and no doubt a lot of vibration. Your nornal reaction to that wuold be to throttle back, which would only increase the out of balance condition. Other than maintaining full power until you are within gliding distance of an airport and then stopping the engine for a dead sttick landing, I cannnot think of to much else to do. Any ideas?

Re: Throttle Cable Break

by bill martin » 14 years ago

bill martin

10 757 0

Joe,

I have thought about that scenario myself and came to the same conclusion you did. Stay at full throttle to keep the engine balanced, then shut down to land. I have seen engines where the throttle springs are reversed so they go to idle if a cable breaks. I think I would prefer full throttle so I could go somewhere. I had someone suggest using a solid wire push/pull throttle with no spring at all. My only problem with that is that you don't know where the throttle is going if the wire breaks. I think the factory setup offers the best of a bad situation.

Bill.

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Re: Throttle Cable Break

by Roger Lee » 14 years ago

Roger Lee

131 5.38k 5.44k

This has been discussed on another forum. This is a good check if you are ever in flight and all of a sudden the engine feels like it's shaking itself to death. Your first instinct is to pull the throttle back which you will do, but let's say that only makes matters worse. So the next quick thing to try is to go wide open throttle to see if it gets worse or it smooths out. If it smooths out you know you have either broken or some how become disengaged between the cable and one carb. If you have not removed or damaged your throttle arm springs then when the one cable became disengaged from the carb the spring took it to wide open and the other carb was back at whatever position you had the throttle set. So one half of the engine is trying to run at 5100 rpm and the other at 5500 rpm (as an example). The right and left halves of the engine are running at different rpms. When you went full throttle then both carbs/rpm equaled out again.
Now if you set your carbs up to run the rpm between 5500-5800 rpm then you have a 5 minute time line to land and or shut down. If you have it set at 5500 rpm and I know some of you less then you could run this rpm all day to a safe landing site and then shut down and land.
Here is another good example of why you need to do a good pneumatic sync on your carbs. This of course is a very extreme example, but you kind of get the idea of what vibration can be if the right side is not at the same rpm as the left side. The cross over tube can only do some much and then it's vibration time. This isn't good for the engine in the long run. You can't always feel the vibration unless it gets fairly pronounced, but your engine can tell the difference.

Pneumatically Sync those carbs

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

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