That's very interesting. I just checked mine and it does not have a sensor. It has a raised nipped with a hole in it that looks like it would accept a sensor but no sensor. This nipple is about 4-5 inches ahead of the udder, towards the front of the bike on the right hand side. My arrow full system is in transit. Will this be an issue? The exhaust may have come with a hole as well, but not be plugged like the factory one.
I think that you are describing the test port for an exhaust gas analyzer. There should be a small plug on both headers, several inches away from the exhaust ports on the heads.
On the S2R1K, the O2 sensor is located on the left side of the udder, just below the engine. I suspect it would be in the same location on the S2R, if there is one.
