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engine keeps sputtering and backfiring when giving gas or under load

I have a briggs and Stratton 23 ohv engine on a john deere zero turn 425 mower. It ran perfectly last week. went to start it this week to mow and now it sputters, black smoke and backfires all when trying to give it gas. it will not run fast nor can I engage the blades as the load makes it do the same thing and cut off. I changed the plugs, cleaned the carb, checked the valves, the blades move freely. It starts up and will idle and run on the lowest throttle setting but it will not do anything else. As soon as I try to push the throttle to fast and engage the blades it goes crazy. I don't know what else to try.

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is there water in the fuel perhaps? Black smoke usually means to much fuel, backfiring, can be to much air via vacuum leak. Don't think it would be a vacuum problem though. Have you checked your air filter? As that can cause over rich mixture and the problems you're facing.


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It’s running rich which is probably due to something wrong with the choke. If you can get the air cleaner off and look at the choke, is it open when the engine is running? Another way this happens (too rich) is the float needle in the carb isn’t closing, so the carburetor is flooding the engine. This happens when a little bit of dirt gets stuck on the top of the float needle so it can’t close.

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I had similar problem and tried every resource I could think via internet…I asked knowledgeable friends …checked valves, replaced carb, shear key,plug…idled up and sometimes blades would engage.and thinking it might be water in the fuel I changed gas and oil….that’s when I discovered that my oil didn’t look right. Apparently the previous carburetor had let gas get into the oil and that’s why the blades wouldn’t engage !!

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that is not a valid problem solution. period. the oil can only come into contact with gasoline during the combustion stroke. then it will exit via the exhaust valve


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john sarà eternamente grato.
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