What's wrong with my riding mower?
June 15, 2010 5:45 PM   Subscribe

My Craftsman riding lawn mower was belching white smoke and barely crawling forward this evening, so the lawn did not get mowed. In examining it, the air filter looks nasty, and the belt I can get to without disassembling stuff feels very loose. That belt appears to drive the blades. It's an 8 year old mower with a B&S engine The belts are original, and the air filter might be too. I don't remember when I last changed it. I change the oil and sharpen the blades in the spring and the thing just runs. It had be running OK, but a little rough, prior to today. My question - it is likely a simple tune up and new belts fixes my symptoms? If odds are it is something more complicated I'd rather just get it fixed by a pro and be done with it. I can handle the simple tune up, but if it's likely to be in vain...
posted by COD to Home & Garden (11 answers total) 1 user marked this as a favorite
I doubt the belt had anything to do with it.

Stuck choke or oil getting into the cylinder (bad rings?)...

my best guess...
posted by HuronBob at 5:57 PM on June 15, 2010

Best answer: If your air filter is clogged enough you could be drawing a vacuum in your cylinder when you should be sucking a fuel/air mixture into it. That would cause you to pull some oil up past the piston rings and give you the white smoke you're seeing. Or your pistons or rings might have gone the way of all flesh. Try taking the air cleaner off and starting it and see if it runs alright. If it does, replace the air filter.

Replacing the belts wouldn't hurt, but that's not going to be killing your power the way you describe.
posted by Kid Charlemagne at 5:59 PM on June 15, 2010

Best answer: If the air filter is really clogged, it will have roughly the same effect as running with full choke. Does the smoke it's belching smell like fuel? If so, cleaning the air filter might well improve things.
posted by flabdablet at 5:59 PM on June 15, 2010 [1 favorite]

Best answer: I wouldn't bother with a tune-up just yet. You're looking at a $65 belt if it is for the mower deck. Start with cleaning or replacing the air filter. As it is an air cooled, gas engine, "belching white smoke is not a good sign. It could simply be a case of it running rich due to a clogged air filter. See if this fixes the problem of rough running and whether it performs the way you want it to from a power standpoint. If it does, change the mower deck belt. It is long overdue. Lastly, is this a hydro-drive mower or does it have a clutch for moving forward and reverse? If it is hydro, you probably have a drive belt up underneath that needs changing too. This involves dropping the mower deck and spending an afternoon uttering words you never thought would come out of your mouth. Oh, and another $45 belt.

If, after changing the air filter, the engine is still smoking badly, it is bidding you a fond farewell. You could take it to a lawnmower repair shop, but it will cost many dollars to rebuild the engine or do a valve job.
posted by Old Geezer at 6:05 PM on June 15, 2010 [1 favorite]

This happened to me when a neighbor changed the oil for me and overfilled the oil. At least, that's what my dad said the problem was. It was annoying for awhile but it stopped when the oil level dropped.
posted by not that girl at 6:36 PM on June 15, 2010

Losta smoke usually means something to do with oil. i mean check everything else too, but check oil first, Possibly a gasket bleed?
posted by timsteil at 6:38 PM on June 15, 2010

Response by poster: The oil level is fine - I checked that. It's a clutch driven engine. I'll change the air filter tomorrow and see what happens before I invest in the belts. Thanks for that tip.
posted by COD at 6:40 PM on June 15, 2010

You might want to make sure that one of the mower deck spindle bearings hasn't seized up and put a really heavy load on the motor. If you disconnect the deck drive belt from the motor do the blades spin easily ?

Also, many clutch-driven transmissions have their own drive belt, and as it gets older it can slip, causing you to go slower, but you should smell burning belt in that case. I know before I replaced my belt it would slip off if I jerked the clutch, leaving me stranded until I took the thing apart and put the belt back on.
posted by rfs at 7:40 PM on June 15, 2010

Did it make a terrible burning rubber smell? I have had this happen several times when something clogs the blades. Like, you know, a giant stick. I don't know what kind of idiot* would ride the mower right over a giant stick, but there you have it.

What happens is the engine spins the belt, but the belt is unable to spin the blades. So instead it whizzes fruitlessly over the blade turner thingie, and makes a terrible smoke. Think of spinning your tires in a parking lot, or a vacuum cleaner belt.

My procedure is to lie down and reach under there. I first feel the blades to see if they spin freely. Sometimes they do not, having seized up with rust or whatever. WD40 fixes this in the short term; in the long run they need to be properly greased.

Next I try to scrape out any big wads of grass. Sometimes if some lazy jackass* waits too long to mow a spot and it gets too long, the sheer volume of cut grass will clog the blade.

Finally I feel all around for anything that could be stopping the blade. Sometimes this is obvious, like a giant stick. Other times it is not so obvious. Once it was a koosh ball. (Where the fuck THAT came from, I have no idea.)

Also check to make sure the belt is in the right track. The last time I had to replace a belt, it had sort of fallen out from where it was supposed to be, because a metal flange thingie** had rusted out and come loose.

* Me

** Yes, that is exactly the phrasing I used when I requested a replacement part from the Ace Hardware guys
posted by ErikaB at 10:48 PM on June 15, 2010

Before you do anything else, change the air filter and spark plug. That should only cost around $15 total and will probably allow it run like a top again. I don't think the belts are usually super tight, as it doesn't take a lot of friction to turn the blades. If the belt was slipping, you'd smell it.
posted by cp7 at 6:36 AM on June 16, 2010

Response by poster: I fired up the mower without the air filter installed and it runs fine. So the clogged air filter was the problem. Yea me for a cheap fix, although the air filter for this engine is 33 fracking dollars, and has to be ordered. The morning after I posted this we woke up to no hot water. That turned out to be a $15 part, so I dodged 2 expensive bullets this week. I'm not sure if I should live in fear of the third problem, or run out and play the lottery :)
posted by COD at 4:18 PM on June 17, 2010

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