I have a lawnboy 10685 mower about 4 years old. It began to surge last fall and I had it rebuilt by a shop during the winter and the problem continues. It surges, then I stop it when the bag is full and it will not restart for awhile. It appears to be overheating. I took it back to the shop and they pulled the screw in gas jet on the side and said it was plugged, apparently from mowing in a dusty area. They blew it out and and it worked for about 15 minutes and will not correct itself, even when I take out the jet and blow it out. The air cleaner, spark plug are ok and the oil is fresh and full.
I hope that the shop didn't rebuild the whole mower engine for you if you took it in for a surge. If you mean they rebuilt the carburetor, that's what it needed. I'd call them, tell them it's doing the same thing as it was before (starving for gas, causing the governor to "hunt"). The carburetor is dirty inside. You have a blocked/partially blocked jet. You can either take the carb off yourself and try to clean it, or take it back to them and let them try again.
Here is a thought. First, before you take it back to the shop, take the small bolt on the bottom of the carb. This holds on the bowl. You do not want to take this off if the machine is full of gas, cause it will leak all over your mower/floor. Tilt the mower backwards or try to drain the gas out. When you get this little brass bolt/nut out, and get the gas cleaned up that leaked out, if you look real hard you will see a very tiny little hole in the shaft of this little bolt. Some even had 3 of them. It may appear to be just a blemish in the finish, but it has to be clean to allow proper operation. Spray with carb cleaner, and take a small wire, such as a single strand of a speaker wire or something similar. Clean that hole/holes out. Clean out the inside of the bolt shaft as well, as debris will settle in there. Put the bolt back in and tighten the bowl up. Make sure the bowl is straight and the gasket is back on the little brass bolt. Tighten snuggly, but not forced.
Try that. If it works, and the mower runs better, put some carb cleaner in the gas and run a bit.
I have a 10550 gold series Lawn boy that ran fine for 8 years then it started surging, it also started leaving a puddle under it after it sat all week, and became hard to start, I had to push the primer bulb more times than usual, and had to run with the choke partially on for awhile to keep it running, I read several references to increasing the jet size, but it used to run great, why would the jet size need increased after 8 years of great service, so, I finally assumed that the lower crankshaft seal must be leaking, allowing more air to get into the crankcase so it would rev and then the governor would slow it back down(surge) , this would also explain the puddle on the floor(excess fuel would leak out of the crankcase while it sat idle), after changing the seal, the surge problem is gone, the puddle is gone, and it starts very easy again with little to no choke and only 2 pumps pn the primer bulb when cold, I hope this helps someone else!!
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Did you have anything done to the carburetor?
Jim
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