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Marvel Schlebler Floats for Rotax Engines

n233va

Member
Hi All

I installed the MS floats on Oct, 3rd. Out of the box the pairs weighed over 7 gms. , 7.46 and 7.42 to be exact. I called MS and inquired about the weight and the fact that Rotax specifies no more than 7 gms. Was assured that they tested these and they worked at that weight. So I installed. Today Oct 27th, in route to Marana AZ. The engine started running rough, intermittently. The exhaust gas temp on the right carb side would drop by 200 to 300 degrees. After a brief period of time all ran smooth and the temps returned to about a 40 degree split. I turned around and headed back to Prescott, AZ. On the way back, I had repeated instances of intermittent engine roughness. Each time, the exhaust gas temp on the right side would drop at least 200 degrees and there was a rather strong smell of gas in the **** pit. Upon return, I dropped the bowls on both carbs for inspection. The right set of floats appeared to be sticking slightly. If I gently shook the bowl they would release and float normally. The exhaust was black and oily. I replaced the MS floats with a usable set of Rotax floats in both carbs. Upon run up, the engine ran smooth but above 4000 rpm's the oil pressure dropped dramatically. I shut down and dumped the oil. It was evident that there was gasoline in the oil. I also removed and drained the filter. Closer inspection of the MS floats compared to the Rotax floats revealed that the hole in the floats for the pin were smaller in the MS floats and did dot have a brass sleeve as the Rotax ones do. It is my opinion that the MS floats(s) on the right carb stuck and flooded the engine with raw fuel. When they became un stuck due to vibration they floated again for a period of Time.

I replaced the oil in the engine with fresh Aero Shell Sport Plus 4 an rand it up again. This time, oil pressures were normal and remained so through 5000 rpm static on the ground.

Based on my experience, I would strongly caution against using the MS Floats. My hope is that the cylinders were not washed enough by the fuel to have caused any damage to the walls. Compressions felt normal but I will get gauges on the tomorrow. And bore scope the cylinders 1, 3 . Wanted to get this info out asap.

If you have questions, I can be reached at [email protected]. If you leave a phone number I will be happy to call you back.
 
What kind of fuel were you using? 100LL? Auto 91 with 10% ethanol? Auto 91 without ethanol?
 
Question - did you run the electric fuel pump for any length of time prior to engine start, or for that matter, after engine stop? Normally not a problem and in fact desirable, but if float sticks, perhaps electric pump could cause carb overflow into intake manifold and if intake valve was held open - raw fuel could entire cylinder.

Be a stretch - but possible...
 
Hi All

I installed the MS floats on Oct, 3rd. Out of the box the pairs weighed over 7 gms. , 7.46 and 7.42 to be exact. I called MS and inquired about the weight and the fact that Rotax specifies no more than 7 gms. Was assured that they tested these and they worked at that weight. So I installed. Today Oct 27th, in route to Marana AZ. The engine started running rough, intermittently. The exhaust gas temp on the right carb side would drop by 200 to 300 degrees. After a brief period of time all ran smooth and the temps returned to about a 40 degree split. I turned around and headed back to Prescott, AZ. On the way back, I had repeated instances of intermittent engine roughness. Each time, the exhaust gas temp on the right side would drop at least 200 degrees and there was a rather strong smell of gas in the **** pit. Upon return, I dropped the bowls on both carbs for inspection. The right set of floats appeared to be sticking slightly. If I gently shook the bowl they would release and float normally. The exhaust was black and oily. I replaced the MS floats with a usable set of Rotax floats in both carbs. Upon run up, the engine ran smooth but above 4000 rpm's the oil pressure dropped dramatically. I shut down and dumped the oil. It was evident that there was gasoline in the oil. I also removed and drained the filter. Closer inspection of the MS floats compared to the Rotax floats revealed that the hole in the floats for the pin were smaller in the MS floats and did dot have a brass sleeve as the Rotax ones do. It is my opinion that the MS floats(s) on the right carb stuck and flooded the engine with raw fuel. When they became un stuck due to vibration they floated again for a period of Time.

I replaced the oil in the engine with fresh Aero Shell Sport Plus 4 an rand it up again. This time, oil pressures were normal and remained so through 5000 rpm static on the ground.

Based on my experience, I would strongly caution against using the MS Floats. My hope is that the cylinders were not washed enough by the fuel to have caused any damage to the walls. Compressions felt normal but I will get gauges on the tomorrow. And bore scope the cylinders 1, 3 . Wanted to get this info out asap.

If you have questions, I can be reached at [email protected]. If you leave a phone number I will be happy to call you back.

I?m guessing MS has indicated they will follow up? I?ve got two pair waiting to be installed.
 
MS Floats

91 Octane with ethanol. Electric pump on continuously. Have not contacted MS at this time. Event occurred today 10/27. Will contact on Monday. I plan on asking for a refund and return the floats. Let you know the outcome of my communications with MS.
 
Slow day here and I've been thinking about this long-running float problem. I wonder if floats could be made from a hollow plastic blow mold... sort of like plastic soda bottle? Plastic would have to be resistant to gasoline and alcohol. I would imagine if the float was hollow the plastic wall thickness could be sufficient and still have good buoyancy. The brass slider tube would need to be incorporated into the molding process. Envision a bobber used for fishing - very buoyant.

Are the new MS floats a solid material or are they hollow as I describe above?
 
MS floats solid?

Solid. MS has video showing a float being sawed in two and still working.
 
Solid. MS has video showing a float being sawed in two and still working.

Solid - that's what I thought. I have emailed Marvel-Schebler with suggestion to make floats with hollow injection mold technique per post #6 above.

I'll post response soonest...
 
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