It could also indicate a blockage or obstruction in the PILOT JET of the carb (also referred to by various other names like "slow jet", "low speed jet", "idle fuel jet", or even other unprintable names when it gives trouble). Because the pilot jet has a much smaller orifice than the main jet, the pilot jets are more apt to "catch" a small piece of trash than the main jet. Particles that can clog a pilot jet may very well pass right through the main jet. Because the pilot jet has such a tiny orifice, blobs of water can "stop up" the hole as effectively as solid debris. I personally think that if the fuel pump were at fault, or anything else that would affect "MAXIMUM fuel flow", the problem would not be what you describe (removing the load from the engine and reducing throttle to a slower position). If you had a problem related to maximum fuel flow, you would experience things like "it runs OK at idle and will throttle up to high RPM but when I engage the deck, the engines begins to slow down and run rough after a few seconds. If I disengage the deck, the engine soon speeds up again. Or "It does OK until I go up a hill (or other scenario where load on engine increases). In regard to fuel pump at idle RPM versus high RPM: Pulse vacuum fuel pumps have a "relatively flat" output volume at any given RPM. This is due to the time allowed for the pump diaphragm to "react" to the "pressure to vacuum" oscillations of crankcase pressure. At idle RPM, the pulse changes occur fairly slow, so the pump diaphragm is able to move a greater distance with each pulse, because it has enough time to move the greater distance, thus it will move a certain volume of fuel in a given PERIOD OF TIME. At higher RPM, the pulse pressure to vacuum changes occur more often (because of the greater speed of the engine pistons). At higher RPM, the fuel pump moves LESS FUEL PER PULSE, but because the pulses occur at a FASTER RATE, the net output volume of the pump (during the same time span) is about the same as at idle. The volume capacity of the pump is always engineered to be well above the actual requirements of fuel flow needed by the engine anyhow. In operation, the fuel pump will fill up the carb bowl to the "float level". When the float level is attained, the needle valve closes and no more fuel is allowed into the carb until enough fuel is consumed to let the float drop a bit, at which point, additional "make up" fuel is allowed to enter the float bowl. During the times that the needle valve is closed, the fuel pump diaphragm IS NOT MOVING, because it now has a "head of positive fuel pressure" against the diaphragm, preventing it from moving at all. This is the nature of diaphragm type pumps. Carburetted engines are always running "off of" the fuel in the carb bowl at any given moment of operation. If you are running a carburetted engine that uses a fuel pump to transfer fuel from tank to carb, and you "pinch off" the fuel hose to the carb, the engine will not react immediatly to that action (by dying). It will continue to run on the fuel already in the bowl, until it consumes that "finite volume" of fuel. Water in the carb bowl (and other places in fuel system) might be to blame for the problem you are having here. A good clean out of carb and fuel tank (and a new fuel filter) might fix it. The auxiliary tank could certainly "rule out" any concerns about fuel pump performance, but I doubt a fuel pump max flow problem because THAT would cause problems during times of HIGH fuel requirement (cutting or towing heavy) and not when the engine load becomes "lighter".

cuppla things before blowing the moths outta yer purse.. operate the tractor. When the engine cuts out, be prepared to quickly check for spark at the plug(s). If no spark, likely that yer coil is crapping out when it gets heat-soaked. You could also pull the engine shroud sheet metal off, clean the fins well and inspect any revealed wiring for insulation damage... blocked/dirty fins will also promote engine overheating & related probs..

"9. All safety mechanisms have been tested and/or bypassed. " Exactly HOW did you bypass the seat switch? That may be the root of your problem. Best way to make sure any safety switches are out of the circuit is to disconnect the kill wire at the magneto. Is the carb fuel solenoid energizing? This post was edited by bill_kapaun on Tue, Jul 1, 14 at 20:16

I have the problem of carbon building up quickly on the sparkplug. Can anyone tell me what causes this and how to prevent it or at least slow it down so I'm not continually cleaning it or replacing the spark plug during one season of mowing. I was once told that it's a problem with the fuel being too rich. I use the premium fuel; I do not use ethanol fuel in the mower.