Sometimes when I shut down my motor it wants to run on or "deisel" just a bit, It has only done it about 3 times of the 10 to 12 times I have ran it. Usually, I would assume the timing is a bit off. But I am only familiar with american iron. Is this a reasonable assumption? The motor is an 84 or 85 with fuel injection. As an aside, what does the pop-off valve do on the airbox?