"I was thinking this has something to do with a stuck float in the carb"
Well, kind of.. Probably a speck of crud in the carb needle/seat or a punctured float.

There is probably crud stuck in the carb, but it also sounds like the lower seal may be leaking. If it's only the seal, that can be fixed relatively easily, but with that motor I believe that sometimes the seals are failing because the bearing has worn and allows too much play on the shaft. If that's the case, I don't know if I'd put any time or money into that motor.

Gas is definitly leaking thru the carb float valve. On the floor can be coming from the muffler or the el under the deck. It would be nice to know the model number so we could see which engine we are talking about.

Leaking seals will not empty the gas tank of course. This engine would have needle bearings which do not normally fail that quickly.

Anyway, you need to add a gas line shutoff valve, if it doesn't have one, and use it even when you get the leaking float valve fixed.

Walt Conner

Constant RPM or failure to accelerate could be just because it's running too rich. It also could be clogged exhaust ports or a stuck air vane. With the engine running, take a stick and push on the air vane under the shroud from the left side of the mower. It should move freely and the engine should rev. If moving the throttle lever doesn't make it run faster, look to see if the throttle wire is making the sliding lever on top of the carburetor move back and forth, and that the little spring connecting the lever to the base of the air vane is there. If everything is okay so far, you may need to put more tension on the governor spring. Find the disc at the base of the air vane and turn it four clicks clockwise. Start the engine and see what that accomplished. If you start to get some throttle response, give it four more clicks. You should stop when it runs fast enough to cut grass at full throttle and throttles back to a good idle. If you can check RPM, top speed is 3200. You said it was a 'Silver Series', which would have the 'V' engine with muffler under the deck. If the muffler is above the deck, it's a 'Silver Pro' with a 'Duraforce' ('E') engine. This is important because the Duraforce throttle lever goes into 'choke' if pushed all the way down, and the 'V' engine doesn't have a choke. Sometimes people don't know about the choke and push the lever all the way down to run, then complain about the smoke and poor performance.

Like Saxman says above. However, if none of this checks out, there is another possibility on the slow erratic running that I don't believe has been mentioned. This engine has a 2 stage electronic ignition. IF the "Run" phase is bad it will run but poorly on the "Start" phase at about 800 rpm.

Walt Conner

Thanks for all the input. I have added a gas line shut off but only as a temporary measure - good idea to use permanently though. It is a Silver Pro - the muffler is above the deck. Also, thanks for the input on the choke - you can definitely feel if you go to choke on the throttle lever - there's almost a detente there.
I replaced the throttle cable last season - all was good there. I will definitely be trying your tips out in the next few days - keep 'em comin'!

walter,

The two stroke Lawn-Boy with the duraforce engine is prone to this leak down problem because of marginal float and inlet valves. A small partical of dirt can lodge in the inlet valve of the carb and cause the valve to leak fuel into the crankcase and then out the "U" bend tube under the deck. In the worst cases the muffler gets some raw fuel in it too and then when the engine is started a bunch of uch comes spraying out. I had one Duraforce do a rich surge last season, this is when the inlet valve is passing too much fuel into the carb bowl that it drains up in to the engine while running and creates a over rich running situation. The engine acted just like a lean surging engine (which the duraforces are know for) except it smoked a lot. To fix it I replaced the float, inlet valve and cleaned the vent/primmer system. I found that the primmer system can and does allow dirt into the carbs float bowl. I suggest that you also fit an inline fuel filter along with a inline fuel shutoff valve. Now if I can just remember to use the shut off valve. Once you get the fuel system sorted out you can set the RPM's, I set mine at 3100 RPM's and all is well.