Q My Yamaha R1 is buzzing... but not in a good way
When I turn the ignition on for my Y-reg Yamaha R1 I can hear the fuel pump start up, but the EXUP valve doesn’t move and there is just the sound of a buzzing, arcing, noise from the EXUP motor. The EXUP valve itself is turning freely and when I turn the EXUP motor with a pair of grips it does reset when I turn the ignition on, but then it just sits making the aforementioned noise. Mojo67, MCN forums
Answered by Charles Marvell, Flitwick Motorcycles The EXUP mechanism is sited in the most hostile environment on the bike with rainwater, dirt, salt and heat combining to attack it, and the slightest friction in the EXUP housing will be enough to stall the valve. Although you say it is turning freely, can you flick it through its range of movement with your fingertips? The valve blade can get out of alignment and the only surefire way to recover its profile is to spin it up on a lathe. Maybe a previous owner had to use heat to loosen the bolts and that has been enough to distort the housing too, so you may need to polish that as well.
Sounds like the blade on your EXUP valve has gone out of alignment