Off hand open end discussion. I certainly don't have all the answers just some theories.
Where does that bubble come from?
One possible place for sure is inlet exposure to air while engine is running (upside down to the left). But then you have to think, How long does it take to empty that line (idling or revving)? How long to refill after upright? Is there any residual air remaining in the system even after fill tube is full? Why is there a bleeding procedure required during PDI in the first place?
I think Polaris designed a oil bottle (unique in the industry, 2 chamber design) that LIMITS the possibility of open end feed for a short period of time anyway. I like it and the effort to make it. Truly needed on a mountain sled.
Is there another place the bubble can come from (if you think weird like me lol)? Why are there check valves? Is there pressure any place in the bottom end of a 2stroke? What is the designed "pop" pressure on the oil side? Will air next to this valve make the same pressure as oil in specific sized tube?
If feed is restricted (say the tank is not vented at all) can a bubble come from the bottom up? Can a feed restriction end up creating bubbles in the distribution lines from cavitation? Can a check valve fail, siphon, or leak? Why does my sled smoke so much on start-up? What happens to the bubbles when the engine is in reverse?
Does it matter if there is a bubble in the feed line?
People who have bled oil systems during PDI have watched these bubbles move along. Sometimes one or two can be stubborn at the bends even with pump lever at max and rpm up. Very little movement after the flow has been divided after the pump. Do different feed lines flow more than others? Can that cause one or two or three bleed lines to be more difficult to purge, take longer?
If you never crack the bleed screw to fill the feed line, it takes much longer, so you always do, to get rid of a bubble in the feed line and not reintroduce it to the distribution lines. But,,, that bubble in the feed line disappears quickly when allowed to flow.
Does that mean a bubble in the feed line creates a restriction to flow? Shouldn't at WFO. Why does it stay there for some? Or does it go and come back for the same reasons as it appeared the first time?
One OEM vents the tank specifically. Costs more so why. Was it research or just carry over of design?
2 use a simple oil cap that is specifically (gravity and a ball) designed to work properly in a horizontal position. It's worked for years but two have experienced more "mysterious" bottom end failures since using oil bottles with the caps mounted on an angle. Most people carve to the left more than the right lol.
The present oil pump system has been around for a long time. RPM and lever position dictated total flow. Used to be set richer than today so big puddles internally and excess was the norm. But,,, people still noticed straight ratio premix to be more reliable. It was because there is always a delay before the crankcase rebuilt it's "puddle" that is safe and required in two stroke.
Today they all leaned then out for the EPA but Doo uses the most at WFO. It uses an electric pump. Two strokes need oil. It's still splash lubrication.
I'd like to know how the electric pump works on the AXYS. Is it full bypass flow, metered to pass EPA area, then excess at WFO so it doesn't need to wait until the "puddle" grows in the crankcase?
I think the oil cap on the AXYS is mounted horizontally again too,
