Sinking New-Style Carb Floats

by David HEAL in 912 / 914 Technical Questions 8 years ago

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Re: Sinking New-Style Carb Floats

by RotaxOwner Admin » 8 years ago

RotaxOwner Admin

59 1.58k 14.4k

If you read the Service Letter link above carefully, you will see it states

"The repair or replacement of Products or the performance of service under this warranty does not extend the life of this warranty
beyond its original expiration date."

However, that is modified slightly by the clause below:

For non-certified/non-certificated Parts that are not installed at the time of delivery of a new and unused Engine by a Rotax
Distributor/Dealer, this coverage is for the first EIGHTEEN (18) CONSECUTIVE MONTHS OR THE FIRST ONE HUNDRED
(100) HOURS OF OPERATION, whichever occurs first.

Here is an example...

An 912 UL engine's original warranty is this:
For non-certified/non-certificated four-strokes UL Engines (912 and 914 model designations), this coverage is for the first
EIGHTEEN (18) CONSECUTIVE MONTHS OR THE FIRST TWO HUNDRED (200) HOURS OF OPERATION, whichever occurs first.

So basically, if your original UL float needed warranty replacement in the first 18 months OR 200 hours, it would be eligible for warranty replacement. But the 'replacement' float would only be replaceable under warranty up until another 18 months or 100 hours of operation had passed. A 'warranty replacement' part only carries an additional warranty of 100 hours of operation (although the elapsed time warranty is the same - should the warranty replacement part fail within 18 months - but say there had only been 99 hours of operation, it would be replaced by another, and the warranty time 'cycle' for that part would start anew...)

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Re: Sinking New-Style Carb Floats

by James Stricker » 8 years ago

James Stricker

16 90 106

What is so difficult about making floats that "float"? It's not like this is the first carburetor ever built. Floats should be good for the life of the product. Cars up until last ten years or so, motorcycles, snowmobiles, boats, Lycoming / Continental aircraft engines, you name it, all had carburetors with floats. I can't recall ever seeing a problem as pronounced and prolonged as this...

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Re: Sinking New-Style Carb Floats

by Bill Hertzel » 8 years ago

Bill Hertzel

13 1.95k 7.97k

What is so difficult about making floats that "float"? It's not like this is the first carburetor ever built. Floats should be good for the life of the product. Cars up until last ten years or so, motorcycles, snowmobiles, boats, Lycoming / Continental aircraft engines, you name it, all had carburetors with floats. I can't recall ever seeing a problem as pronounced and prolonged as this...

Back in ancient times before fuel injection, floats were commonly a bubble of air surrounded by metal.
The two halves of the float were stamped out of copper or aluminum and then soldered or welded together.
If the floats sunk, it was because they had a leak.
You could fix the leak and drain the float and be back in business.
The metal floats had a lot of reserve buoyancy. They floated high in the fuel. And were easy to quality check.

Modern floats are commonly made from molded, closed cell, foamed plastic.
They do not have a lot of reserve buoyancy.
They float low in the fuel and are hard to quality check.
The tiny bubbles in the foam are not supposed to connect to each other. Closed Cells. (Think, Soap Bubbles.)
If they connect together during molding, Open Cells, you end up with a sponge instead of a float.
They will slowly soak up fuel and eventually sink.

The Metal floats were impervious to fuel.
Plastic is permeable to fuel if not formulated very specifically.
The lighter components of the fuel can actually pass through the walls of the plastic bubbles, eventually filling them and sinking the marginally buoyant float.

An option not commonly seen is to coat the foam with a material impervious to fuel. Epoxy? Teflon?

The best, but impractical way to test the plastic floats is to submerge them in fuel for a year or so and then weigh them.
The other option is to Trust the people that mold them and ship them to the field.
If they don't fail they are good.

We used to call this the field QA test method.
There is nothing inherently wrong with this method.
It is done thousands of time every day in thousand of products.
In this case, Bing lost the bet twice in a row.
The odds were long against a double failure, but even at 50 million to one, someone will win the lottery.

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

Thank you said by: David HEAL

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Re: Sinking New-Style Carb Floats

by James Stricker » 8 years ago

James Stricker

16 90 106

Thanks for the history - stuff I pretty much already knew. What we're really talking about here is a safety-of-flight issue.

Even though Rotax chooses to use a motorcycle carburetor it must be airworthy and not operate in a state of deteriorating acceptability with use and calendar time. Regular scheduled maintenance should be all that is required to guarantee that a critical system is operating at original design parameters. Its unconscionable to put critical replacement parts into the field that are of unknown quality. It doesn't matter that gasoline permeates foam bubbles and that quality control is dicey at best. What matters is safety-of-flight.

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Re: Sinking New-Style Carb Floats

by Guilherme Tomazini » 8 years ago

Guilherme Tomazini

6 13 21

If you consider it costs 50 times more than a similar motorcycle float. It should NEVER EVER fail. It should be the highest quality float in the observable universe.

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