Engine vibration at low RPM after hot restart

H. Paul Shuch is a Light Sport Repairman with Maintenance ratings for airplanes, gliders, weight shift control, and powered parachutes, as well as an independent Rotax Maintenance Technician at the Heavy Maintenance level. He holds a PhD in Air Transportation Engineering from the University of California, and serves as Director of Maintenance for AvSport of Lock Haven.

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roger lee
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Re: Engine vibration at low RPM after hot restart

Post by roger lee »

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Last edited by roger lee on Thu Aug 06, 2015 3:08 pm, edited 2 times in total.
Roger Lee
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FastEddieB
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Re: Engine vibration at low RPM after hot restart

Post by FastEddieB »

I don't believe dieseling was ever reported by rcpilot.
Fast Eddie B.
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roger lee
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Re: Engine vibration at low RPM after hot restart

Post by roger lee »

Sorry, I got the post mixed up. The leak could cause the engine quit at low rpm.
Roger Lee
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3Dreaming
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Re: Engine vibration at low RPM after hot restart

Post by 3Dreaming »

FastEddieB wrote:I don't believe dieseling was ever reported by rcpilot.
He didn't , but it did enter the conversation in post #3.
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Re: Engine vibration at low RPM after hot restart

Post by rcpilot »

From what he showed me it looks like the connection to the intake manifold (on the carb side) came loose causing a small air leak.
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Re: Engine vibration at low RPM after hot restart

Post by 3Dreaming »

rcpilot wrote:From what he showed me it looks like the connection to the intake manifold (on the carb side) came loose causing a small air leak.
A carb flange failure?
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Re: Engine vibration at low RPM after hot restart

Post by rcpilot »

The rubber flange came loose where it attaches to the carb.
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Re: Engine vibration at low RPM after hot restart

Post by 3Dreaming »

Since I maintain aircraft with Rotax engines it would be interesting to know the age of the aircraft , and if the flanges were replaced at 5 years as recommended by Rotax.
roger lee
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Re: Engine vibration at low RPM after hot restart

Post by roger lee »

I believe he means the carb was not secure in its mount. I have seen a few people come to my shop with the carbs not in the socket and one finger would push them out of the socket altogether. The rubber flange and carb have an indentation that kind of pops and locks it into place. The carb must be pushed all the way into this socket area before the clamp is tightened. You should be able to grab the carb with your hand and with some force try and move it around and it should stay put.

I haven't seen any of the bolts that hold the rubber flange in place come loose. When you replace the flange it does have an "O" ring between the flange and the metal air intake.

I have seen two flanges over the years that were actually split. These are usually old flanges and flanges that didn't have the 8mm clamp spacer on the screw and then they became over tightened. These splits are hard to find unless you grab the carb and use some force to wiggle it in its socket to make the split open up and is usually found while it's running.
Roger Lee
Tucson, Az.
LSRM-A, Rotax Instructor & Rotax IRC
(520) 574-1080 (Home) Try Home First.
(520) 349-7056 (Cell)
3Dreaming
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Joined: Sun Jan 10, 2010 6:13 pm
Location: noble, IL USA

Re: Engine vibration at low RPM after hot restart

Post by 3Dreaming »

I recently had one that was separated from the metal base.
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