The start and end code tab isn't available if you're using an UM2/UM2+ machine unless you switch the "Gcode flavour" in the machine settings in cura. I wouldn't do that unless absolutely necessary.
The amount of priming is set in the firmware for the UM2 so you'll have to re-compile the firmware if you want to change it.
Have a look in Cura under the tab called "Start/End-Gcode"
If you click the start.gcode file, you will see some lines of code that always gets added to the top of your gcode after slicing (it eg. homes the printer, zeros some values, stops the fans etc.)
There should be a line saying something like:
G1 F200 E3 ;extrude 3mm of feed stock
The number after the E is the amount of filament (in mm.,) extruded before the print starts, play around with that value.
Don't turn it off completely, the hotend needs to be primed so that process is not happening during the printing of the first layer... Otherwise you will get terrible bottom quality and adhesion problems.
I always print with 3-5 lines of skirt, which performs kind of the same function (It starts the print by printing lines at a certain distance around the perimeter of your model), but also will let you do a bit of "on the fly" bed leveling before the actual print starts...Edited by Guest
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