Briggs & Stratton 10M902 Surging

[Merkava_4]

Craftsman Push Mower Model: 907388920
Craftsman Serial Number: 112905M023952
Briggs & Stratton
Model: 10M902
Type: 0489 E2
Code: 05101754

This is the little vertical shaft L-head with the plastic Pulsa-Prime carburetor. Engine is surging very badly. Everything is in good shape and clean. New carburetor 795475 installed today. I cannot find any air leaks anywhere. No air leaks around carburetor. No air leaks from intake manifold tube. Carburetor is installed properly. Gas tank is spotless inside. Gasoline is brand new. Makes no sense whatsoever. I've never experienced anything like this before. I've replaced carburetors on this push mower numerous times before. Each time the mower would fire up on the first pull and run perfect.

 

[Coupe]

Check the governor spring has not been streched or out of shape if
it has one also thee idle jets not a wee bit blocked.

 

[hacskaroly]

Does this unit have one of those air vanes that adjusts as the mower heats up? If it is hindered might be an issue. You say that everything is new, so I am assuming the air filter is new too? I am one of those who never changed the air filter and wondered why the mower ran like crap.

 

[Merkava_4]

This one has the mechanical governor driven off the camshaft. They call it a governor / oil slinger. It has flyweights and little paddles to sling oil. It has a gear to mesh with the cam gear. Thanks so much for replying hacskaroly and Coupe. I truly appreciate the help.

 

[EFSM]

Does giving it more fuel help? Try choking it by putting your finger over the intake partway. If that easily smooths it out, it is running lean. If that doesn't easily fix it, then it is governor related. It could be that it needs a static governor adjustment, which is performed by loosening the governor arm and turning both it and the shaft wide open before tightening again. Or as mentioned it could be a spring issue.