Originally Posted by Greg2012FLHTK

I asked Nightrider the maker of the VIED & XIED why you need Xied FL-XIED-10 with the cat or FL-XIED-10TFF without the cat or why they recommend a 50% setting with the cat and 25% setting without the cat on the VIED. This was the reply I got: "Generally the VIED's want settings around the 25% rich area once the converter is removed. This is actually to compensate for reversion bringing fresh air to the sensors (which is seen as a lean mixture and actually adds some fuel), so the VIED needs to be 'turned down' some to compensate. The net effect is you are still running (and adjusting) to get the ECM to run in closed loop at 14.0:1, but you have to back off on the VIED settings to stabilize the voltage readings with the lower settings because of the fresh air that can get to the O2 sensors with the converter removed" So apparently removing the cat actually makes the bike run richer not leaner as most people believe. They also recommend the FL-XIED-10TFF or running 25% on the VIED if you keep the cat in but change to slip-ons with larger then a 1.75" baffle.