Surging - where the engine speeds up and slows down - is caused by a lean fuel air mixture. The carburetors built after Sep 1997 were not adjustable or equipped with adjustable needle valves. Mixtures can be adjusted with replaceable jets located inside the carburetor. If the carburetor was rebuilt correctly, there are other things to check. If the fuel tank is mounted higher than the engine, remove the fuel line from the carburetor to see if fuel flows freely. Aim the fuel into a jar to see if there is dirt or water present. Flush any debris from the end of the fuel line before reattaching. Another check is to connect a vacuum gauge to the carburetor fuel fitting. This section of the carburetor is actually a vacuum operated fuel pump. Crank the engine to see if suction is present. If there is no suction, check the vacuum hose connection from the the crankcase. Sometimes the hose ends become cracked and vacuum is loss. Is the fuel tank in the rear of the tractor? Assuming the fuel pump has suction, attach the vacuum gauge to the end of the fuel hose to see if the fuel line is good. sometimes cracks form in the fuel line and air is drawn in. Look for cracks or loose clams on all fuel connections. Look for dirt and debris in the fuel tank. If the fuel lines are good, check the gaskets around the intake manifold to cylinder. A lean fuel air mixture could also be caused by worn valve guides - but is not likely on the opposed twin. Most likely there is still some dirt in the carburetor. If the float is the plastic style and the float has warped, the fuel level in the float bowl is too low. If the person who rebuilt the carburetor used fuel to wash the parts, the carburetor could still be varnished. A carburetor spray must be used to clean the internal parts.

Sounds to me like a battery or starter problem. Try putting a few drops of oil on the starter shaft where it exits the starter body at the top, make sure it can run down inside the bushing. Make sure all battery connections are clean, bright metal to metal. It would have been better if you had given the model number of the engine since there are several different 18 hp B&S engines. Walt Conner

Murray riding mover was running OK. Took a short break and came back to start up and when I turn the key...nothing. Took the battery out and had it checked--its good. Replaced the fuse and tried again but when turning the key...nothing happens. Any ideas as to why to try next. I thought it might be the ingition switch but that looks pretty hard to replace. Anything else before I try that?

OK, the chunks may be the result of moisture etching material out of the casting surfaces of the carb/fuel pump. I know I have seen black junk in the jet well of these carbs and thought that stuff may have sloughed off the inner liner of the fuel hose. I have also heard of some types of "fuel eating algae" that can cause a black slime to appear. Strange world indeed!