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

[eyedempotent]

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:
https://plus.google.com/photos/1096...s/6006248339054947985?authkey=CPXa-ezDpd_w_gE

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.

 

[Mikel1]

Needs a carb cleaning. The reason why it's running better with the old air filter is because of reduced air flow. The new one has more airflow than the old dirty one.

 

[eyedempotent]

Thanks so much. I got some carb cleaner today, watched a video, and cleaned out the carburetor. Now it seems to run fine. The gaskets and seals looked fine, I forgot to run a paperclip through some of the narrower gaps like the video said to do, but it seems like it's running okay. I usually put fuel stabilizer in the lawnmower over winter but I may have forgotten to do that this year.

 

[exotion]

Just make sure you get it up to operating temp every few weeks and you won't have to use stabilizer. Glad you got it working and glad you did it right. Some people would have just used the old dirty air filter because it work. Dooming the engine

 

[eyedempotent]

Thanks. Is there any advantage to doing it that way over stabilizer? I'll do a search on this next question (it's a loaded one) as I'm sure it's in a sticky or a FAQ but I wonder if there is other maintenance I should do while I'm at it? Fuel filter issue? As I said the hoses and seals that I could see in and around the carburetor seemed fine to me.

 

[exotion]

Spark plug, oil, air filter sharpen blades or replace. And keep it clean you'll be fine and keep up with the fuel