Well, There is nothing wrong in the Logic, It's following what you ask to do.
When you double Tap it's it's activates the logic of jump since it is already stated and you have also give a condition to bring chain saw out when double tap.
How to resolve
Creat a global variable Tapcount
If single Tap then set variable to 1
if Double Tap Then set variable 2
If Variable Tapcount is = 1 then jump
If variable Tapcount is = 2 then Bring chainsaw
since variable are set and with exact match they will only perform action according to the variable.There is a gesture options for touch "Tap" and "Tap-Double" get a reference on manual it will also help!
Or simple solution create to sprite buttons jump and kill and use them.
I hope it helps! if you any question feel free to ask!