Quote:

Can someone tell me what good are the speed bleeders? I've put them on and was under the impression I didn't then need to submerge the tube.



Right.
That's what the internal check valve does.
But, it's a mixed blessing.
Since it takes a bit of pressure to open the valve, a system that's been fully evacuated may not do it.
That's likely what's giving you trouble.

Said Molly to James, that's a fine motorbike. Richard Thompson