Volvo Penta MD7A started but shut off
I have an MD5B. I would have to guess it is air. I could not get mine to start for anything after I bought it, and finally resorted to a little squirt of starter fluid in the air intake. I was told never to do this by the fine folks on this forum and others, but after using the same method for years growing up with a John Deer farm tractor, I thought I would give it a try. Been running ever since. Your mileage may vary.