@Carlos G all of the 4:2:1 Spyder exhausts of that design have the same issue and have for the 15 years we've been using them. L&R don't blend until the tip, and you'll find that with a tailpipe sniffer you can get it into one side or another, BUT you can get some odd readings at times, plus you will get a huge influx of fresh air sucked back into the exhaust when you lift off the throttle. you can get a descent tune this way, but nothing beats having o2 bungs further up the system, just before the mufflers is my preferred spot.