Can anyone tell me what this (see photos) is on my Massey Ferguson MF 1726E? It's on the right side, below the oil fill cap. It seems to be a cap or a valve in a rubber tube. I think the cap had a tab on it so you could use your fingers to turn it. But the tab may have broken off when my metal funnel fell against it. Either as a result or a coincidence, the tractor will not start now. It cranks fine, but does not fire. Any thoughts?