Cold Start Lever AFR Effects
Here is a plot of AFR for my '04 R1150RT cold started with the throttle and cold start levers in three positions. Ambient temperature was 35 F.
1) For the left hand third of the plot, the cold start lever is on, the engine is idling smoothly and the AFR is in the 12s. Notice that the mixture is appearing to get slightly richer in the first 40 seconds. This is because the fuel is being atomized and burned better, leaving less oxygen in the exhaust. Less O2 is interpreted by a wideband oxygen sensor as a richer mixture.
2) In the center part of the chart, the cold start lever is abruptly switched off. At first the mixture seems rich due to less air going in. But after a few cycles, with less air going through the TBs and the engine still cold, the rich mixture isn't atomized as well, the engine misfires, and the O2 sensor reads the un-consumed oxygen as a leaner mixture. I will say that a different way: there was enough fuel but not enough air and all the fuel didn't burn, leaving unburned O2 in the exhaust which was read by the sensor as leaner.
3) Cold start lever still off but throttle cracked open for smooth idle. Better combustion so the AFRs return to the 12s as the fuel and oxygen burn more completely.
Bottom line: cold engines need more fuel AND a bit more air to idle well. The oil temp sensor reading tells the motronic to add fuel, the rider uses the cold start lever to add air.