Lawnmower runs with old air filter but sputters to stop with new

I have a Troy Bilt 21" 6.5 HP lawnmower that's a few years old. It's been running strong, but I've neglected maintenance for a while. So recently I did a little work on it. The first thing I tried was changing the air filter. Right after putting in a new filter (it's the paper type) the lawnmower would start but immediately sputter to a stop. Then when I put the old air filter back in (it was pretty dirty) it runs just fine. I don't know a lot about engines, but this seems to indicate something about a carburetor air/fuel mixture. But I don't see a choke or any way to alter that mixture. I've done some searching on this site and others and there are a few ideas and similar problems but I was wondering if anyone has seen this behavior before and can explain it?



If it helps I've posted some pictures of the lawnmower here:

http://ift.tt/1imo5w9



If it matters I afterwards changed the oil, the spark plug, and the blade. But the results were always the same: runs with old filter but not with the new one. Any suggestions? Thanks.