actually, there is validity to his statement. you need to sniff within a foot of the exhaust port. you want to monitor burned/unburned fuel--- not the mixture plus fresh air. the mufflers have a blocking plug in them so he wold have to drill for the probe to pass thru. i used to weld a bung onto the pipe and screw in a nipple i could connect a hose to and sniff the hose to get a proper afr reading. remember o2 and co and hc are measured in parts per million, so an accurate readind is essential for the best tune if yo are shooting for a certain afr.