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I just bought a 2008 toro z5000 with a Koehler courage 21 engine. It ran a little rough and wanted to die when I bought it. I cleaned the carb, put a new plug, and changed the oil. Now it will mow, and does great until it hits even a slightly thick area. Also when I really bog it down, or when I just throttle it down as I do every time before I kill it, it will blow smoke. It appears to be blue, and I can smell it burning oil occasionally. It did leak oil before I made a new valve gasket, so it could be residual on the smell.

How do the spark plugs look (read) ? Any signs of burnt oil on them ?

7394 said:

How do the spark plugs look (read) ? Any signs of burnt oil on them ?

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This is with only one mowing ~30 minutes or so on brand new plug.

That plug doesn't look very good for just 30 minutes. And the blue smoke on idle down I would say sounds like loose valve guides. As the higher vacuum nearing idle can suck oil down the guides.

a "Leak Down" test would be good to confirm my opinion. Or even a compression test, then add a teaspoon of oil into cylinder & test compression again, if readings stay close to dry test, it's top end guides.

7394 said:

That plug doesn't look very good for just 30 minutes. And the blue smoke on idle down I would say sounds like loose valve guides. As the higher vacuum nearing idle can suck oil down the guides.

a "Leak Down" test would be good to confirm my opinion. Or even a compression test, then add a teaspoon of oil into cylinder & test compression again, if readings stay close to dry test, it's top end guides.

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Interesting way to test. I'll break out my compression tester tonight. Will this cause a loss in power or am I just still not getting enough fuel? Mower idles a little rough on low throttle.

solefate said:

Interesting way to test. I'll break out my compression tester tonight. Will this cause a loss in power or am I just still not getting enough fuel? Mower idles a little rough on low throttle.

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It's old school test, my Dad taught me about 45 years ago.

Loose guides won't cause power loss, is your air filter clean ?

As to rough idle, I've had good results adding some Seafoam* to the gas (follow directions) , & using 100% gas is best. And your low idle shouldn't be much less than 1,500 rpm's.