you could just change it with the storebrand you have , take it complete just change the crank pulley (if its a 160 not 125) 125's had the spark plug offset not in middle .
g4's arent that bad , and seems your gunna need to learn soooo , why not now ? just slow n easy and a few there to compare if you get lost in plastic parts . hardest part is the cutout i think , getting them to work can still sometimes be tricky as the odd one just wont play the game !
