Unfortunately the search function is down so I was unable to locate information. I'm installing a different non standard engine in my kitfox. Since I'm already past the point of no return (engine and most crucial items purchased motor mount built etc) I'm not going to get into a debate about it being a good idea or not. So I'm not going to say what kind of engine. For the purpose of this thread I believe the only crucial bit of info is that it is fuel injected and uses a high pressure fuel pump. The only other hint I will give is that it's not a Subaru. The aircraft has a 6 gallon tank in the right wing and used to have a tank mounted forward of the instrument panel that was removed for cg reasons (heavier engine). The plan right now is to mount a 6 gallon cylindrical spun aluminum tank mounted in the location shown in the screen cap. It will be a header tank meaning the fuel will drain from the wing into it with the fuel pump near the outlet on the bottom. The green line is the path the fuel travels to get to the engine. The yellow line is the fuel return line for the fuel injection. I'm concerned mostly about the need to vent the header tank. In my reading made difficult by the non functioning search option I've come up with concerns why it should be vented and why it shouldn't. Reasons why it should be vented 1. When filling the tanks if the header is not vented might take an awfully long time for the header tank to fill from the wing tank. 2. If for some strange reason the line from the wing tank gets plugged fuel can't flow from the header and the engine quits. Reason why the header shouldn't be vented 1 not sure if this one is possible but if the vent to the header pressurizes the tank enough to prevent fuel from the wing from draining into it I may have had another reason not to vent the header but if I did I can't remember it. The other question is regarding the fuel return. Due to the folding wings and there not at present a convenient port to run the return line to on the wing tank it would be nice to run the return line to the header tank and hopefully if there was still fuel in the wing the fuel pump would have enough pressure to force fuel back up the line to the wing tank. That does however negate the possibility of a filter between the tanks, and Ive read many comments about the existence of such filters. In a pinch I'm considering running the return line to the lower sight tube port. For those of you wondering if the header is in the cockpit, yes it is. This fox will only be a single seater. Brackets will be welded in to mount the tank. So what are your thoughts?