on about wet sumping . on my es2 all the oil pipes are of the clear type to see if the oil is going where it should, anyway as i was checking the bike over after a run i noticed the oil slowly draining down inside of the rocker feed pipe after about 5 hours or so it had completely gone then i noticed a spirit level size bubble appearing in the pipe to the oil feed side of the oil pump close to the engine after a time the oil emptied from that. i have a manual oil tap on the tank so when its turned off whats in the pipe remains there until the bubble appears then the pipe empties. my thoughts are is whats happening because air is entering the pipe work aerating the pump then oil can flow over time emptying the tank. without the air in the pipes would the oil remain in there, a bit like drawing fluid up a tube and putting your thumb over the end the fluid remains until you remove your thumb. so wondering would none return valves in the rocker and oil tank return pipes help in any way, any thoughts. don't all attack me at once 
Barry
Don't think the presence…
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thanks for the info John.…
thanks for the info John. it was just a theory i had. yes see what you mean about the bubble in the petrol pipe ive seen that before.
Barry
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Don't think the presence of air changes things eg the wet sumping occurs because of the height of the column of oil from the feedside pump up to the level in the oil tank minus the route to the big end and the alternate route from the feedside gears though the shafts to the scavenge side and in to the sump. If you put a non return valve in with a spring just strong enough not to open under this column then the wet sumping stops. I have tested this when I made mods to a non return valve to reduce the risk of no oil.
Note you could have a huge flat oil tank with gallons of oil inside and it would apply less pressure on its outlet than a thin pipe full of oil but higher than the tank.
What you have highlighted is that the pipes get air in them from maybe a leaking joint and then when the engine is started the gear pump sucks on air not oil and engine failure follows if the oil does not get into the pipe. Even though you see air in the pipe there will still be a thin film of oil on the ID of the pipe allowing the oil still to get to the sump over time. If you use clear pipe to feed carbs with petrol you see the same bubbles with an engine running but the engines will still run as fuel is still moving inside the pipe but only on the inner surface in the opposite direction of the air.