Filament not feeding then eventually blocked I have an ANET A2 Prusa - which I've setup and performed a few prints on and they have various problems with the quality.  I'm after some specific experience on what the flow of filament should look like or if my decription triggers someone  

I've been adjusting settings - In particular the temperature - as the filament seemed too fluid as I could easily cause a large spurt of molten plastic by manually pushing the filament with very little effort.  

So I reduced the head temperature to 195 and all seemed better 

However after a time - I noticed on a longer print that the feeding was sometimes failing with the filament jerking back as the feeder slipped off it 

The stepper did not appear to slip back just the gear skipped on the filament
It appeared to cause a problem in the print with a few of the lines being missing before it started extruding normally again

I increased the temperature back to 200 - however the issue continued intermittently however I left it and when I returned the head had become blocked with the final part of the succesful print consisting of very thin hair like extrusions and eventually stopping completely

The head is flooded and I need to clean it out 

So my questions are - how runny should the filament look when the head is at the correct temperatures, is the extremely runny filament I saw at 200 obviously too hot - or is that normal or at least have people seen it looking like that when successfully printing?

Initially , before I reduced the temperature,  I doubled the skirt and that seem to make a good enough print 

Does anyone have  experience of why it can seem to be printing but then slowly start failing until the head becomes blocked?
From my experience with mk8 extruders lower than optimal nozzle temperature or clogged nozzle can lead to an extruder's stepper motor overheating and partial burning out of a stepper

It looks like “Achilles' heel” of mk8 extruders. I had to change 4 stepper motors for 2 3d printers with mk8 due to that

First symptoms – skipped steps. You could also check a temperature of your stepper – next symptom is a high temperature of stepper motor after several hours of printing

My fix for this issue – adding cooling fans to stepper sides and top (3 fans). It significantly reduced overheating and hopefully a life of stepper

Another solution of this issue can be in using of a stepper motor with gearbox to increase torque on a filament gear, so no high torque needed from stepper itself

About printing temperature, it depends on plastic which you are using

I’m using ABS plastic with an optimal printing temperature from 230-260 Celsius degree. For my current plastic supplier optimal temp is about 255 Celsius degree

To check the optimal temperature for your plastic you can print one box in different temperatures depending on Z position and found the optimal temperature by the z position of surface with the best quality. You can find code samples how doing it here

If a temperature is too high then this part of the box will be bloated, if it's too low - you can see the gaps. Here is the video, which illustrating this for PLA

UPDATE:

The issue was in the low temperature of printing. After calibration and setting temperature by calibration outcomes to 200 Celsius degree printer started working well

However, please be aware of the fact that wrong printing temperature can not only decrease the quality of printed things, but also can lead to wear of your printer parts and even can break it