Can't figure out how to upload a .capx but this is the answer
Global Number "Movement = 0" 1= Move 0 = Don't move
System>>Movement=1 >>Simulate 8Direction pressing left
Keyboard F is down >> System Set movement 1
Keyboard F released >>> Set movement 0
Basically what your doing is when you are holding down F your setting a global value to 1 then when you release the button your setting it back to 0.
Since 1 means to move left and 0 means to not move the system works.
Just make sure the first system has a Everytick.