If you take the backplate off you will find that all you can see is a large counertweight attached to the crankshaft with a left hand threaded slotted screw. In front of that is a caged needle bearing that supports the crankshaft against the backwall of the combustion chamber. That's why I made the statement that the nipple is only there to vent excess oil. When reassembling note that the backplate will fit in any one of six positions. Thus the nipple in question can be pointed down up or to either side. This makes it easy to change the position of the carb and muffler in relation to the radial mount if need be. Of the three that I own I noticed that the nipple in question pointed in a different direction on all of them when I acquired them. So it must not be a fine point in assembly. Actually, I did tie my nipple back to the tank once but after seeing all that oil being pushed back to the tank I removed it. I figured my oil content might be approaching 50% by the time I got to the bottom of the tank, and it wasn't clean oil either.

I have built a twin PBY with Wankels. They idle within a couple 100 rpm of each other and tach together pretty well across the full range. I've gotten it wet twice but it has yet to fly. It appears that the Wankel is all RPM and no torque so the slightest amount of spray in the prop is enough to stop an engine. I haven't given up yet though.

As for poor idle. My experience says that is most likely caused by broken tip seal springs. The engine will still develop most of the rpm expected but will not idle at all. The reason being that at high throttle the seals are sealing by centrfugical force while at idle they lose contact with the walls and thus compression is noticeably absent except on maybe one out of three revolutions. A set of tip springs costs $4 and can easily be replaced by removing the front cover. Don't pull the rotor up to get to the tip seals. There is a chance to get it out of time if it skips a tooth on the gear. (Not meaning that it's very hard to get back in time) Slide the tip seals up and out and check the leaf springs. There should be two behind each seal and they will pull out with the tip seal. To replace them slide the tip seal in position and slip the springs in behind them. A needle works well to press them in to their trapped position. You will hear a slight "click" when they snap into the seat. Reassemble the front cover and fly it. I threw away all the phillips screws and replaced them with socket heads. The proper size is 3X23 mm. Buy the 3X25mm socket heads and cut the excess off with a dremel cutter after you reassemble it. The tip seal leaf springs are the weakest point in this engine. I would bet 2 out of 3 out there have broken springs. Expect a noticeable improvement in idle and a possible increase of 1000 rpm on the top. Seems to help mileage too but I have no solid numbers. BTW I have been told peak torque (if there is such a thing with a Wankel) is about 14,000 rpm.