Muffler Corrosion (small hole...less compression?)

[Canuck]

Hey guys i was running over the GZ with a fine tooth comb to find any leaks in the exhaust to try and figure out why my gz is running so poorly in the low gear range. (shifting and idle and pulling in low gears sucks lately.. )

and i found a hole that you could stick the end of a pen into(just alittle one) but enough that i could feel some air puffing out onto my hand. I know this is not meant to be.. my question is could it be enough to screw with the GZ mixture and overall compression..

The hole is located midway down the body of the muffler on the underbelly.. Ill post pictures shortly.