Craftsman Briggs & Stratton Mower Surging & Running Low RPM

So I bought a brand new Craftsman push mower last spring. It has the 5.5 Gold Series Briggs & Stratton engine. It ran fine all last year. This year it has started surging. Aside from not running smoothly, it doesn't cut as efficiently,as a result. Yesterday I took off the muffler, intake manifold and carburetor (I'm not a mechanic, just a tinker). The carburetor looked really clean, but I cleaned it out with some wire anyways (nothing came out). The gas collection bowl thing wasn't sludged up at all. I then noticed that the spark plug was really fouled. The tip and the insert were pitch black. I have since found out that having too much oil and not enough gas causes this (I did overfill the oil last late summer/fall and it was shooting out large plumes of white smoke for a while). I replaced the spark plug with a brand new one, put everything back together and started it up. It seemed to be running "OK", but not perfect. It seemed to be running at low RPM and was bogging down very very quickly. After cutting a very small section, and stopping and starting the mower a few times to test things out, it went back to surging like it was before and the engine still seems to be running "rough", with a slight almost metallic noise.

I'm not a mechanic by any stretch of the imagination, just good at Googling and watching youtube videos lol.

Any ideas on what would be causing this? I'd rather try and fix it myself rather than spend $100+ dollars to get it serviced. The mower itself was only a little over $200.

Thanks!

Have seen this almost everyday this year and I suggest replacing the float needle and seat to solve the problem. Here is the procedure I use.

Needle and seat replacement

Remove the carb, and then remove the float bowl. Check the float bowl jet (which is the bowl screw) and make sure the jets both horizontal and vertical are clean and open. Tip the carb upside down and remove the float pin and float with needle attached. Look in the float needle passage and you should see the red float seat at the bottom of the passage. This is where a #5 crotchet hook would come in handy as you need to remove this seat. If you have no hook, but compressed air, you can blow through the fuel inlet and try to pop the seat out. Put your thumb over the passage to prevent the seat from flying who knows where. No air or hook try bending a stiff paper clip to dig the seat out.

I would either give the carb a good 24 hour soaking or have it ultrasonically cleaned at this time.

With the seat out clean the passage way with carb cleaner. Now you must find a drill bit slightly smaller than the passage way, to be used to press in the new seat. Apply a very, very small amount of a very light lube to the new seat. 3-1 oil or lighter, to help seat it better. Carefully insert the new seat in the passage way with the rings on the seat down toward the carb body. Slowly and carefully force the seat down with the back end of the drill bit. Once it is seated, check to see that it did not flip and the rings are up. *Next check to make sure that the float does not have any liquid in it. *If it does, replace. *If everything looks correct, attach the new needle to the float and install with the float pin centered. It everything is correct, the float should seat level to the carb body, when looking at it upside down. If everything looks good reattach the float bowl, making sure that both the bowl gasket and the nut gasket seal properly. Reinstall on the engine and test unit. Remember to have patience and take your time. Good luck, but I don't think you'll need it.

PS: *On the side of some Tecumseh carbs you will find a plastic cover. *Under this cover will be an idle jet. *Remove it and check to see that the jet is open both horizontally and vertically. *You should be able to push the old float needle wire through the vertical opening.

Where would you recommend that I acquire a new float needle and seat? And, if you could, what exactly do you mean by "seat"? I believe I understand what the float needle is, it's that thing inside the float bowl that is round and comes to a point...but the seat I have no idea haha.

Also, what should I soak the carburetor in? Are there just bottles of liquid carb cleaner I can buy?

If you post your engine numbers model, type and code I can give you the exact part number for the needle and seat. My guess would be part number 398188, but I cannot be exact without numbers. The seat is in the seat well which the needle rides up and down in. These two parts close off the fuel flow, controlling the amount of fuel in the float bowl.

Surging is caused by engine starving for gas and governor opening throttle to keep speed up. 1st try Seafoam or injector cleaner in the gas and run it. The new stuff is so EPA lean that the least bit of varnish in the teeny passages will cause trouble and the ethanol(water) gas exacerbates varnish formation and actually corrodes the cast aluminum. I use only water free hi test gas to which I add Stabil so's wont have trouble.

Can you list the model numbers from the engine. It would help identify parts needed.

On some of these engines when the carb' is removed, there is an orange O ring in the manifold block. This often expands and needs replacing, it should fit snug in the grove of the manifold block.

Good luck, Phil