Bought A Rotax 912is Engine New Fuel Pump Assembly Isn't Usable . What Would You Do?

[jdmcbean]

Thanks for that, the picture is extremely helpful. Was the mounting pattern the same? I believe the firewalls come pre drilled from Kitfox. I just looked at Edge Performance and their dual pump setup goes for $1,600 shipped. I'd have to look into compatibility but it's a possible option. The input and output out are on opposite ends so I'm not sure how much that would affect the install with the pre made hoses. Lots of research in my future. The newer Rotax assembly looks pretty stout. Thanks

Keep in mind? Rotax wants the pumps to run in parallel and not in series. The reason from Rotax is for pressure and amperage. I do not think any of the aftermarket pumps are compatible electrically and are running in series not parallel.

The Kitfox housing fits in the same location and fuel routing as the original Rotax housing. The pumps are larger and are NOT off the shelf Bosch pumps. Rotax contracted Bosch to build pumps for them that was not a grounded housing. So the pumps housing is not electrically grounded to the pumps connector. Rotax wants to keep the engine from chassis ground after engine start.

[ADK-Flyer]

Keep in mind? Rotax wants the pumps to run in parallel and not in series. The reason from Rotax is for pressure and amperage. I do not think any of the aftermarket pumps are compatible electrically and are running in series not parallel.

The Kitfox housing fits in the same location and fuel routing as the original Rotax housing. The pumps are larger and are NOT off the shelf Bosch pumps. Rotax contracted Bosch to build pumps for them that was not a grounded housing. So the pumps housing is not electrically grounded to the pumps connector. Rotax wants to keep the engine from chassis ground after engine start.

Thanks for the info it really helps with my decision making process. I'm definitely leaning towards getting the Rotax pumps even though the cost is higher. I want to stay with the theme of reliability and safety on my build. That is the exact reason why I wanted a Rotax engine to begin with. Nothing against other platforms and all of the innovation that's going on with Yamaha and other engines that people are using in experimental is just amazing and I definitely considered it because of the tinkerer in me. I just think with my lack of experience and heavily wooded terrain in the Adirondacks where I live being one of the largest forested area in the US I really leaned more towards something proven. You just aren't flying over a lot of farm fields or a lot of open areas in general other than lakes and ponds. I'll just have to work a little harder to get what I need to achieve it LOL.

[jiott]

John, when I look at the photos of the Rotax pumps the old ones on the left sure appear to me to be plumbed in series. The new ones on the right also appear to be plumbed in series although its a little harder to tell from the dark photo. You say they should be in parallel so I am confused.

[Eric Page]

The 912iS fuel pumps are plumbed in series. See the diagram in the 912iS Installation Manual, section 73-00-00, page 3 (page 105 of the PDF).

[Dave S]

This might require a bit more thinking.

If a person looks at the actual pump (the old one where we can see where all the stuff connects) we can see where the fuel would flow in the event of the failure of one or the other of the pumps.

Consider if pump 1 fails - let's say it got plugged up for one reason or another so fuel can't get through the pump - where would the fuel flow? In a simple series configuration the flow would be stopped entirely. Enter the check valve - if the #1 pump gets plugged up, fuel can flow around the pump through the check valve to pump # 2 which (hopefully) is functioning and continue to pressurize the system. If pump # 2 gets plugged, and pump #1 is OK it can continue to operate while the check valve allows fuel to flow around #2. The system essentially becomes a parallel config in function.

With a simple series configuration, if one pump or the other fails electrically, but can allow fuel to flow - you still have pressure provided by a second pump - but only in that one failure mode. A simple series config won't protect against a plugged pump.

With the Rotax design - if a failed pump is not plugged, fuel may flow through the failed pump but not be pressurized and/or it may also flow in part through the check valve for the failed pump to the second pump.

In a sense, the system is more like an automatic series/parallel system where the check valves come into play. The check valves allow for series function if both pumps are functioning correctly as well as parallel function if one of the pumps chokes.

If both pumps fail - sorry about that - out of luck.

[Eric Page]

At the risk of being pedantic... If both pumps are running, the check valves do nothing and the pumps are in series. If one pumps dies, the engine is fed by the other one and the failed pump is bypassed by a check valve. Regardless of which pump has failed, that's a single-pump configuration, not two pumps in parallel. As plumbed by Rotax, there's no way to put two operating pumps in parallel with each other.

[Geek]

At the risk of being pedantic... If both pumps are running, the check valves do nothing and the pumps are in series. If one pumps dies, the engine is fed by the other one and the failed pump is bypassed by a check valve. Regardless of which pump has failed, that's a single-pump configuration, not two pumps in parallel. As plumbed by Rotax, there's no way to put two operating pumps in parallel with each other.

Got to agree with Eric on this one. Basic definition of parallel is a common input and a common output and neither the Rotax schematic or the factory plumbing show that. My guess is that this is one of the reasons our pumps are so noisy (cavitating?) when we run them both. Truth be told I start up with both running but shut one down after take off (kind of like the ole Piper electric fuel pump as a back up for the mechanical one). Pumps making that much noise just doesn't seem right to me. Just my opinion on that.

G