Smoking and backfiring

Oldwrencher85

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I have aToro , 42-inch deck Engine : Kohler 7000 series, KT 725, 22 hp.

Serial # 4715806043 SPEC PS KT725 3031 Build date: 6-7-2017. It has the Walbro carb with the Smart Choke system. I bought it from the neighbor, it wouldn't start took the carb soaked it in carb cleaner and blew it out with compressed air. It started right up ran fine. This year, after running for a while it started missing and blowing smoke. After it cooling down it started right up and seemed to be ok, Then same thing again. I took the carb off again, it appeared clean and blew it out again. It is back firing thru the carb, fouling the air filter and appears to be on only one cylinder, since the frame of the mower is black with soot on one side of the muffler. I put on a new ignition module on the suspected side, gaped it at .010 and no change even with the choke blocked fully open. I took the new module and spark plug from the sooty side and switched it to the other cylinder, no change. The gas is fresh and non ethanol. What's next? Must be a mechanical problem ?
 

mechanic mark

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See pages 34 & 35 in your Kohler Engine Manual Series 7000 by clicking above website.
 
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sgkent

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plugged exhaust or mis-adjusted valves would be my guess. Could be a bad spark plug too.
 

Oldwrencher85

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Thanks for your input. I found the exhaust valve was set to .010, the intake at .005. both are supposed to be set at .005-.006. I didn't think that this would cause all the problems. I pulled the head and as I expected, the gasket was blown.
 

CubbyCommando

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I had a similar issue that was the oil pressure sensor. Take a look at my post below. Cheers.

 

Oldwrencher85

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Actually I screwed up by making an assumption. Since there is an exhaust pipe for each cylinder leading to the pancake muffler, I though there would be an outlet for each exhaust pipe from the muffler. Since the muffler is mounted so low to the ground you can't see it easily. After I pulled the head, I got tired of working on my knees and jacked the rear end up and put drive up car stands under the rear tires. Only then could I see that there was only one outlet from the muffler, not two. So I went ahead and installed the new head gasket and found that there was no change. That meant that either the muffler was blocked or the carb was bad. I pulled the muffler and started the engine and saw the smoke was coming from both exhaust pipes, so the carb was somehow blocked. New carb, 39 bucks from China, started right up, no smoke and must have gained 3-400 rpm's over what it used to sound like; the deck really hums. Either the new carb is better, or the old carb was never right even though I thought I cleaned it carefully 2X using carb cleaner, air blasts and music wire in the jets.
 
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