6.25 hp Craftsman push mower - Black smoke & oil from air filter


Old 04-29-07, 02:37 PM
Thread Starter
Join Date: Sep 2005
Location: CA
Posts: 63
Question 6.25 hp Craftsman push mower - Black smoke & oil from air filter

Hi all,

I've got a (about) 5 year old Craftsman 6.25 hp push mower that has been working great until today (used about 3 times this year already). My son was cutting some very very tall, not wet, yard grass (about 6 weeks growth). Black smoke was coming out from the air filter, as was some very small dropletes of oil. The mower was just fine last cuting this season. No work or new oil was added between the two uses. Before this season, I had added (but not changed) oil to the mark, as it was a bit low. Deffinately didn't over-add, it was checked after running it a few minutes. The level was right within the marks and the mower worked as expected for those first 3 times.

The only thing I can come up with that might have caused this black smoke/oil to come through the air filter is pushing the mower hard through the thick grass. Could that be the case? Do you think I could just clean the air filter, dbl check the oil level and try again without fryin the engine?

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Old 04-29-07, 03:03 PM
Join Date: Apr 2007
Posts: 6

It does sound like you over filled it but if thats not the case it sounds like a stuck or broken ring. If it was just black smoke it could be flooding but if you have oil in the carburator its blowing it out the crankcasr breather into the carburator which means you have compression in the crankcase. Recheck oil level but it sounds like a broken ring.
Old 04-29-07, 04:00 PM
30yearTech's Avatar
Join Date: Oct 2006
Location: Central Texas
Posts: 1,176
If your mower was tipped up on the wrong side, or if the engine was rotated while tipped, oil can be fed into the carburetor and air filter area via the crankcase vent. Once a paper air filter is contaminated with oil it will not allow air to pass through it, causing a rich running condition (black smoke). Remove the air filter element and run the engine, if it seems to clear up and run ok without the air filter, then thats the problem.

Replace the element before you actually use the mower to cut any grass or grass and dirt will be ingested into the engine and shorten the life.
Old 07-22-07, 10:21 AM
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Join Date: Sep 2005
Location: CA
Posts: 63
Thumbs up

Thanks for the replies folks.
**** If your mower was tipped up on the wrong side ****
that's exactly what my son had done. I removed the filter, cleaned and dried it the best I could, ran the engine for a few minutes w/o the filter and then replaced the filter. It works fine now.

Just wanted to give a follow up on this one. Thanks again!
Old 07-22-07, 05:05 PM
puey61's Avatar
Join Date: Apr 2004
Location: Upstate New York
Posts: 3,224
Being a 6.5-horse, this should have a paper element air filter and regardless of the method of cleaning you can't possibly clean it reasonably without leaving behind some residue. At a cost of no more than 7 or 8 bucks I'd replace the air filter rather than attempt to clean it.
Old 07-24-07, 12:18 PM
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Join Date: Sep 2005
Location: CA
Posts: 63

Replacing the filter was my first choice, but lack of availability for my model from local retailers (& distance) and ordering online would take a bit longer than my situation would permit + shipping costs, I decided to go with cleaning it for a quick solution. The lawn was in desperate need of a cut, and we were going out of town for 3 weeks. Turns out, the cleaning was effective enough. I plan to do a filter replacement, allowing for enough time to deal with out of stock/not stocked issues and/or purchasing from the internet if needed, along with other 'routine' maintenance next year before the lawn mowing season starts.

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