Overhang printing

I have recently started having problems printing 45deg overhangs and in general the overall print quality has deteriorated.
An image of one of my attempts is attached .



The model is 20mm square and about 15mm tall with one of the Y legs at 30 degs and the other at 45degs. The 30 deg leg prints OK.
I have carried out the following checks
Commanded the extrusion of 50mm of filament and it extruded 49.
Checked extruder temperature from 100C to 200C and good correlation.
Printed at various temperatures from 190C to 220C with little effect.
Changed filament to one which has in the past printed well and whilst there is an improvement it's far from satisfactory.
I recently fitted a Mk 8 extruder and it extrudes smoothly, the fan operates whenever the machine is switched on.
If i watch the printing of the 45deg leg it seems to turn up and then the extruder re-melts it and presses it back down.
The printer is a Mendel 90.
I'm out of ideas.
Any help appreciated

Bobhare,

I've had similar issues in the past and here are a couple of things you could try,

Calibrate your extruder to extrude exactly amount.

Here is a video that might help ...
[youtu.be]

Check your temperature:
Normally HatchBox PLA works best for me at 180c no heatbed on glass coated with Elmers water soluble glue stick

You may also want to consider Slic3r Generate support mattierial is needed.

Bit confused here.
Is this PLA or ABS?
Which fan is on all the time?
I believe the print fan is normally used for PLA but your temperatures seem high for PLA.
What cooling nozle are you using (if any). Wondering if this is due to print fan cooling being blocked by the 30degree brancht. You can test this by turning the part cooling fan OFF then both branches should be the same. Or print with the part rotated and see if the problem changes.