Lawn Mower Motor Issue

[jteneyck]

I have a Toro self propelled walk behind mower, about 8 years old.  It's a fixed rpm motor with no throttle adjustment.  It starts on the first or second pull, but runs rough with low rpm and power, and blows a little smoke for the first two or three minutes until it warms up.  Once it's warm it runs fine, no smoke, smooth and plenty of power.  I only run alcohol free gas in it.  The air filter is brand new.  

What does the brain trust say?

John

[tomsteve]

blue or black smoke?
blue= burning oil. 
black= running rich

[jteneyck]

blue or black smoke?
blue= burning oil. 
black= running rich.

Smells like oil so I'd say blue but it's hard to see so I'm not sure other than the oil smell.  My first thought was one of the valves is sticking or out of adjustment.  It's an overhead valve engine and I've never adjusted them, don't even know for sure if they are self adjusting or not though I doubt it.  

John

[Roly]

Smells like oil so I'd say blue but it's hard to see so I'm not sure other than the oil smell.  My first thought was one of the valves is sticking or out of adjustment.  It's an overhead valve engine and I've never adjusted them, don't even know for sure if they are self adjusting or not though I doubt it.  

John

Try parking it with the rear of the mower a little higher than the front.  A brick under wheel see if it stops it.   A little oil seeping past the rings when parked, do not over fill.   Roly

[MstrCarpenter]

Smells like oil so I'd say blue but it's hard to see so I'm not sure other than the oil smell.  My first thought was one of the valves is sticking or out of adjustment.  It's an overhead valve engine and I've never adjusted them, don't even know for sure if they are self adjusting or not though I doubt it.  

John

Oil draining past valve seals would be my guess. Same result as oil seeping past the rings. Seeing it still runs well enough to cut the grass, I would try some mystery oil in the crank and a little carb./injector cleaner in the fuel. The other thing to check is the auto choke linkage. It may not be opening fully soon enough resulting in a rich fuel/air mixture. On a Briggs it's not really attached to the linkage, the thermostat (Briggs #593208 behind the muffler) just pushes it. Thing is, a rich mixture doesn't really smell like burning oil, and 2-3 minutes isn't too long for a small engine to warm up.

I have a 10 hp B&S on a tiller that blows so much smoke for the first ten minutes that I'd swear it only stopped because the crankcase was empty! Been like that for over ten years. Still gets the job done; right after clearing away all the May flies.

[tomsteve]

Smells like oil so I'd say blue but it's hard to see so I'm not sure other than the oil smell.  My first thought was one of the valves is sticking or out of adjustment.  It's an overhead valve engine and I've never adjusted them, don't even know for sure if they are self adjusting or not though I doubt it.  

John

valves will give signs of needing adjusting. most common is tapping/ ticking sound. i believe OHV are typically adjustable. any change you can get the engine make and model?

Try parking it with the rear of the mower a little higher than the front.  A brick under wheel see if it stops it.   A little oil seeping past the rings when parked, do not over fill.   Roly

pretty much what im thinking. doesnt take much to have the oil flow a bit into the cylinder then seep past the rings.

[jteneyck]

Thanks all.  I did add some SeaFoam to both the gas and crankcase a couple of weeks ago.  Haven't noticed any change.  I'll try putting the rear up on a chunk of wood to see what happens next time I use it, which will be really soon with the way the grass has been growing here.  

I'll let you know.  Thanks.  

John

[jteneyck]

I changed the spark plug today.  The old one was black.  I took the air filter housing off so I could get to the carburetor and found some grass lodged in behind what I call the air vane which I think is what controls the motor rpm.  I cleaned out the grass and lubed all the linkages I could get to for the carb and air vane. The oil level is less mid way between min and max.  

I started the mower with the front pointing down hill and it blew black smoke same as before.  The cleaning, etc. I did had no effect, it still sputtered at low rpm and power for 2 or 3 minutes, then smoothed out and ran perfectly fine.  Sure seems like it's running rich when it's cold.  Any new ideas come to mind, or old ones that are more likely to be the culprit?  Thanks.

John

[MstrCarpenter]

Next time you start it cold, do it with the air filter removed and look at the throttle plate. If it's staying partially closed, hold open it a little and see if the rpm.s pick right up. If they do there's something up with the linkage; either from the vane or from the thermostat. Possibly the carb was removed for cleaning and linkage got put in the wrong hole or there's a spring missing. The thermostat could be working but it's not close enough to the muffler.

[jteneyck]

Next time you start it cold, do it with the air filter removed and look at the throttle plate. If it's staying partially closed, hold open it a little and see if the rpm.s pick right up. If they do there's something up with the linkage; either from the vane or from the thermostat. Possibly the carb was removed for cleaning and linkage got put in the wrong hole or there's a spring missing. The thermostat could be working but it's not close enough to the muffler.

Good idea.  I just ran it before reading this so I'll do that next time.  The carb has never been removed and it ran fine until recently so I don't think anything is out of place, but something could be sticking, partially blocked, etc.  That makes the most sense considering how it behaves.  Thanks. 

John