B44VS 1970

[Rain Dutton]

My engine has a propensity to fill/not scavenge the sump while running. It did this when first rebuilt 12 years past. The oil pump was replaced for an iron 3 bolt and rigorously checked for its pressure outputs as the concern then was that the added Champion oil filter in the return was stalling the pump. The issue seemed resolved however recently sump filling has reoccured. It seems to happen when running slow in traffic.
As the rocker feed is taken from the return would the filter resistance cause the returning oil to take a path of least resistance and return to the sump via the rocker box?
Original cartridges are no longer available, is the resistance of the replacement COF103 101S greater?
Or is there a well known fault and fix I should explore?
Running out of ideas, any suggestions would be welcomed.

[Spaceman]

If the oil filter is clogged then it could well produce enough back pressure to force all the oil down the rocker feed path instead. To check for this, why not simply bypass the oil filter - it won't do any harm not having the filter inline

[rhyatt]

Are you monitoring the oil return to the tank outlet while the engine is running on the sidestand?
If so, the pick up is on the offside of the crank and won't pick up until the sump is filled up