FYI, the ECU uses 2 temperatures to set the A/F mixture. Coolant and intake air temp. Just because the coolant is up to temp doesn't mean that the ECU isn't going to get the injector to deliver an overly rich mixture because the air intake temp is still low. The ECU is calculating the A/F ratio based on the incoming air density, so that means it is using AIT. It will lean things out somewhat for coolant temp, but it isn't a huge amount compared to AIT.
FWIW, I ride my 2012 WR450F in winter up to 8,000 ft. It floods horribly during start up at temps below about 30F. Once it warms a bit it seems OK, but Yamaha is way, way off on the AF mixture during start up. And if you happen to stall it during warm up the ONLY way to get it running is to tow it. I'm guessing that when you tow it the engine spins over above the usual starting RPM and the mixture leans out and then it will clear and fire.
The quick and easy way to get these bikes running warmer without using a thermostat is to put cardboard in front of the radiator.
Edited by MidlifeCrisisGuy, April 11, 2016 - 09:20 AM.