Had post last year on my small Sears riding mower. Ended up completely overhauling it. Now the engine seems to be running irregularly - mainly when I don't have mower blade engaged. It makes an extreme whup - whup oscillation. This seems to almost disappear with the blade engaged and cutting.
Re: 30" Craftsman Riding Mower Model no. 944.601380
Two possibilities at minimum.
1) the Lo idle circuit in the carburetor is partially plugged with debris.
2) a vacuum leak that causes the combustion chamber to get air that hasn't been through the normal passages of the fuel system. Often cause misfire and erratic running because of a greater vacuum at Lo idle than at Hi idle or at full throttle and full load.
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