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I retested the run up once on the ground. Standard run up was fine, however, full power showed the flaw and destroyed my fuel sensor. (High fuel pressure) My hose to the fuel pressure sensor was in contact with the radiator hose which caused the winter blend fuel to boil. I found fuel on the sensor ware the plastic and brass meet. This may not be your problem or help you, but it is something to check. |
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You don't mention the age of the fuel. One time I filled for a trip that did not happen and with weather it was 3-4 weeks of rain until I flew. At 5000' I had one carb blocked and got in some glider time back to the airport. Flushed with 100LL to fix. I used 100LL for winter or when I would not be flying weekly from then on. Other possibility- a few have had starvation in climb out from having the tank overfilled. Fuel appeared to block the new style filler tube vent. Mine would show reduced pressure in climb out with Dynon Betty yelling about low fuel pressure. Drilling a hole in the filler cap (like the original) as a backup fuel vent took care of it.
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On a new motor E-LSA RV-12? How many hours on the engine? Or was it an E-AB motor not bought through Van's? |
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I use a dual filter version on that funnel, I never put fuel in my RV's wings unless it's thru my funnel, peace of mind even though it's a pain and I get odd looks when fuelling! |
Investigation part 1
Hello and thanks everybody for the input so far.
Today my mechanic did the first steps in the investigation: 1) Spark plugs: Dirty, we changed all of them. https://photos.app.goo.gl/FCBgu6razKGMTsTK6 2) We looked into the cylinder: No damage from potential detonation. https://photos.app.goo.gl/zhhho6WCFMtP52DS7 3) Gascolator: clean. 4) Carburetor: Left side: One float was lower than the other. https://photos.app.goo.gl/D7vkeF8mQ8snAi4c8 Right side: Float bowl was connected with piece of rubber to the heat shield underneath (why?): https://photos.app.goo.gl/THHMjWpXqvwy2LWv8 https://photos.app.goo.gl/f5f9cGWWWUgM3CLHA 5) We then looked at the blackbox data at the time of the incident (at second 30) and observed EGR temperature on the right to plummet. https://photos.app.goo.gl/HFFD4v5S8GAEGmgRA Does anybody have any thoughts on a root cause and the purpose of the rubber piece? |
The piece if rubber is fuel tank sealant which Vans specify to put between the float chamber and drip tray - presumably to damp vibration.
I think your problem is that the right cylinders have seen a very rich mixture (hence the black spark plugs) because you most likely have one heavy float which has allowed the carburettor to flood. |
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Post is below. http://www.vansairforce.com/communit...90&postcount=2 |
This is mostly likely an indication that your carbs went out of sync at that point, given that one carb stayed at expected EGT I would say it?s safe to say that you don?t have a fuel system to the carbs problem. But that you most likely have a problem in the carbs.
I would check that you are getting unrestricted fuel flow through both carb fuel inlets - taking of the foot chamber cover and running the electric pump and measuring fuel flowed in the same amount of time (eg one minute) and comparing the carbs can give you a good understanding of that. This is highly likely a restriction in fuel flow, which is either in the carb fuel inlet channel, between the seat and the needle valve. Or contaminants in the fuel bowls and/or in the main jet system. I would also thoroughly clean and lubricated the pistons on each of the carbs and ensure that they are aligned properly ( the rubber gasket has alignment tabs, you and also feel alignment through the inlet throat of each carb. Additionally I would ensure that you have no cracks in the rubber mating flange (carb to inlet manifold). And check that no leaks are possible on inlet side. It?s also likely that you can replicate this behavior or at least see it in data you load to savvy analysis by running your engine at WOT on the ground. If a problem exists you will see the EGTs separate (a 40 F difference seems to be normal on most 912ULS I have seen). |
Felix,
If the right side EGT plummeted at the time of your incident, for sure the right side of the engine went rich. There are only a few things that can contribute to one carb suddenly going rich while the other carb is seemingly just fine. 1. The most likely suspect - one or both of the floats in the right carb have absorbed fuel and are heavier than the published Rotax specification of 7 grams for the pair, causing high fuel levels in the carb bowl, which floods that side of the Rotax engine with fuel. 2. Issue with the needle valve/seat assembly. A piece of crud may have made its way to the needle valve and got stuck between the needle valve and brass seat at the fuel inlet to the carb bowl. Remove the float arm and needle valve and do a close inspection of the needle valve and brass seat. Turn on the master for a few seconds and flush fuel through the carb. Reinstall the needle valve and float arm assembly. Turn the master back on and verify that raising the float arm will easily shut off the fuel with very little pressure needed on the float arm. 3. The float arms are not level – this will contribute to incorrect fuel level in the carb bowl … can be checked by eye … but best to use the Rotax tool/gauge that is used in conjunction with feeler gauges for making an exact adjustment. 4. High fuel pressure - negating the needle valve’s ability to stop fuel from entering the carb bowl. (Unlikely in your case, I should think, because only one carb went rich). 5. A mis-adjusted carb choke on the right carb. Make sure the choke on the right carb is sitting firmly on the metal stop when the choke lever is full in and locked. Verify the choke lever actually locks and holds the choke lever assembly on the stop. The above five potential issues are the most likely causes of a carb going rich. Let us know what the outcome is. Happy flying, |
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