Sudden complete motor failure

by Richard in 912 / 914 Technical Questions 7 years ago

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Re: Sudden complete motor failure

by Bill Hertzel » 7 years ago

Bill Hertzel

13 1.95k 7.97k

The air bubbles in the fuel filters are fuel vapor bubbles and are what gasoline becomes once it reaches the carburetor.
The bubbles are common in filters on the suction side of a pump.
They are common in horizontal and down flowing filters.
You can clear them out manually but they will return none the less. They are harmless.
The will typically be compressed back into liquid state once they reach the pressure side of the pump.
Even if they do not, once they enter the carburetor they just become the vapor that is normally in the space at the top of the float bowls.
Unless the bubbles are huge and occupy multiple inches of fuel line, they will only cause a minor miss at most as they decompress as the pass through the float valve in the carb. Think of what happens when an air bubble in your water line reaches a sink; Only nowhere near as violent.
The engine is not going to stop and the event is not going to last even a quarter second. You will see a slight hesitation at worse.

When the engine slowed to 4000rpm was it missing and coughing? Or just acting like you throttled back?
The float bowls might have gone half empty and then refilled.
Do you have a fuel pressure gauge?

Is this happening with a full fuel tank?
Fuel in the hoses above the fuel level in the tanks are under a vacuum and can draw actual air into the line at any lose connection points.
Removing the Air bubble from the filter may not have been the cure,
But just taking the hoses off the filter and reinstalling them might have been the real solution.

Let us know if the problem returns.

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.

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Sudden complete motor failure

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