How to stop gas from leaking to spark plug of a Wizard I/C 12.5hp 42" 4 speed lawnmower

Make sure that the gasoline if new. You can spray a small amount of starting fluid into the carb to help start the motor. Make sure that you turn the switch to the run position.

could be valve needs set. if it isn't opening at the right time it wont release compression for it to start. it may be the shear key in the flywheel has sheared if you have hit something like a big rock or log or something causing it to die suddenly.

According to Amie Taylor on http://homeguides.sfgate.com/lawnmower-revs-up-down-100220.html "Airflow Issues A lawnmower that hunts and surges may be experiencing something as simple as an airflow issue. If the air that the engine requires to run is blocked, especially sporadically, it can cause the engine to slow down. When the blockage moves or clears, the engine may suddenly rev up in response. To fix this type of problem, check the air filter to ensure that it's not clogged with dirt and debris. Check the vented gas cap as well. Both issues can cause reduced or sporadic air flow, and clearing them will fix the problem.
Spark Plug Problems Another problem that can cause revving and dying of a lawnmower engine is a faulty or poorly adjusted spark plug. Check the spark plug to see if the wire is connected to it firmly and not wobbling about. If it is connected correctly, remove the spark plug to see if it's covered with corrosion. If so, a simple scrubbing with a wire brush can restore it to working order. If necessary, replace the spark plug with a new one. Check the spark plug gap with a spark plug gauge to ensure that it's adjusted to the proper setting recommended in your owner's manual.
Carburetor Adjustment A carburetor that's incorrectly adjusted is a common cause of poor engine idling that results in hunting and surging. Fortunately, most lawnmowers have two screws that allow you to adjust the carburetor yourself. One screw controls the idle speed while the other adjusts the idle mixture. Check the manual if you're unsure of the location of the idle adjustment screws. Start the mower and allow it to run for 5 minutes. Then slowly adjust the screws tighter or looser in turn until the mower runs and idles smoothly.
Fuel Problems A particularly simple fix that can be at the bottom of many lawnmower idling problems is old or contaminated fuel. If the fuel has been left in the mower while it was stored over the winter or while the mower has remained unused, drain it and replace it with fresh fuel. If you have gas-powered blowers and trimmers that use a mixture of 2-cycle oil and gasoline, check to see that you've not placed that mixture in the lawnmower inadvertently."

Are you sure your getting spark? did the plug wire come apart inside the boot? There are a lot of places to go from your question.

there is a fat black wire next to the tin valve cover the plug is under the boot on the end of the wire

Does the lawn mower have spark to plug or plugs ? Simple way to find out ia to remove spark plug & reattach wire to plug & hold elecrtode end up against engine block-(make sure you hold onto rubber or else could get a jolt)-and try to start again, should have spark, if not could be that flywheel strip-(magnet) is rusted over & cannot communicate w/coil to acheive spark. If this is the case simply sand the strip w/180 or 220 grit sandpaper & try again. If you have spark then you are probably not getting gas. Pull bottom scrw out of carb bowl & drain into a cup, check for debris. If gas comes out dirty will probably need to remove float bowl completly. Use care when removing & gasket can be re-used. Clean out float bowl & attachment screw-(has a hole in the bottom which feeds gas to engine) reassemble & try again. Hopefully this information helps.

Have you checked the air filter? Look at the filter and hold up to sunlight if you can't see the light thru the filter then replace.

Replace the battery. Even though the battery may say it's good, it doesn't have enough of cranking amps. Go purchase a battery with 350 cranking amps. This will fix your problem. The battery power isn't enough to kick the starter completely up to turn the engine.

Do you have spark? There are two things to look for when any engine won't start....fuel & spark, Take your plug out and lean it up against the metal of engine...turn it over and see if you see a good blueish spark.

No spark? Could be the plug, safety switch, coil

Next squirt a little gas into spark plug hole, replace the plug...will it fire up? If so...start working your way back down the fuel system....carburetor, fuel lines, fuel filter and gas (is gas old or new? is there any water in it?)

try that...www.nnyparts.com

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