Thanks,
I’ll give it a try

In my previous experience on a fleet of yamaha two strokes all with clear oil line fitted, bubbles in the line of a properly bled and topped up autolube system is not normal.

In a fleet maintenance situation you need to be able to check oil feeds at a glance, not pulling pipes off to see if they are pumping.  This is how we knew instructors had not been doing their job properly topping off the oil tanks..

This engine is making a knocking noise...

You have run it out of oil...

The oil tank is full.  Look here.

Well how do you explain the multitude of air bubbles in the injection line?

Errrr.

Case closed.  Check the tank before every ride or I will get very sniffy with you.

I dont like you when you get sniffy.

I know.  Just top up the oil........

These were not RT3s though, mainly RT100s, TYs of all sizes, and various yamaha two stroke scooters for the on road side.

Did you have the same problem or just rebuilding ?

“Check valve ball and spring are under the small brass spigot. It is a very tight push fit, not screwed in.

 I had to grip mine tightly  in a soft jawed vice this morning, twisting and pulling at the same time.”

Rebuilding. I had my carb off and the oil tank drained itself when the warm weather hit.

Chapter and verse on the two stroke paranoia thread.

Haha, I’m a fully paid up member 

Just pulled it apart, absolutely nothing obvious. Very delicate lightweight spring and a 3.9mm ball bearing. YouTube playing up so can’t upload the video 

youtube.com/shorts/UuOORP5IoOE?feature=share

Yes, bubbles will be pumped down the line after tank is run dry. Trapped bubbles like this one appears to be are something else entirely. You'll likely need to get the pump flow up to clear that one. Running the engine at a medium speed and pulling on cable at pump to achieve maximum pump stroke might force bubble through and line might stay full afterwards. Probably won't though. If you insist on using clear line, get something with correct (very small) ID. Translucent weedeater fuel line comes in a small enough size. Then you might see bubbles travel. Larger line will trap bubbles like yours seems to have done.

Also remember your clear line WILL NOT tell you the pump has stopped pumping.

P.S. Dropping the bike with engine running can introduce air into the lines. Technically the pump should be bled after a fall. Even says so in many manuals.

This really is very different, just impossible to film. I can look down while riding the bike and see the back pressure from the engine almost pulsing in the oil line. Just keeps making think why was the feed moved the other side of the reed valves on later bikes.
Ive got both clear and black oil lines same inside diameter so not thinking that’s the issue 

Remember when I asked if the bubble was more than a couple of mil down the pipe from the outlet?

Clear sign that the pump is no longer pumping. Always thus. The vacuum draws a small quantity of oil out of the end of the tube. This becomes visible when the engine is no longer running.

As I said, we needed to check at a glance.