I hope that you are kidding with us...
Here is your code explained:
tavuka:
PORTA.2=1'<turn on PORTA.2, need 4 osc clock to do that, then next instruction
PORTA.2=0'<turn off PORTA.2 need 4 osc clock to do that, then next instruction
PORTA.4=1'<4 clock to do this, but it doesn't do anything with PORTA.2
PORTA.4=0'<4 clock to do this, but it doesn't do anything with PORTA.2
GOTO TAVUKA '<4 or 8 clocks(can remember) to do this, but it doesn't do anything with PORTA.2
So when you count all clock, you have 4 osc clock long high state on PORTA,2, and 16 clock low state on PORTA.2.
Similar situation is with PORTA.4...
Program execute exactly what you are tell, Not what you want...