These engines are really pretty simple.
They need Spark,Fuel,Compressionin order to run.
Obviously one or more of these is missing.
If you are sure that there is spark on both plugs, then for now we will assume that the spark is ok.
Next, we talk about fuel.
Gasoline CANNOT be used if it is over 30 days old. Old gas will not burn correctly and might leep it from running. Make sure that the fuel is fresh.... als make sure that you are using GOOD 89 octane gas. Regular 87 octane fuel has been causing problems since it has changed formulas.
The last isue would be the compression.
Take the spark plugs out and use a GOOD compression tester to test the compression. If the compression is LOW, then there could be a problem with the valves.
These engines should have the valves adjusted at least every two years or more often.
Usually the clearances are set between '004 and .005" between the valve stems and the rocker arms when the valves are completely closed.
Some of them might have a slightly different setting, but these settings should be good enough to get you going.
Here is a video that should help you try to adjust the valves.
How to set the valves on overhead engines. B & S
Here is the Service manual for your engine (I hope) If this is not the right manual, let me know what your model and type number of the engine and I will find the right manual.
If you need any more help with this, you can contact me here at this question...even after you have hit the "ACCEPT" button to pay me for this answer.
Please click "ACCEPT" or I won't get paid.You may also consider sending a "BONUS" if I have been helpful, Please leave POSITIVE feedback for me as this is how I'm rated. Remember, a neutral is nearly as bad as a negative. If not satisfied, contact me and I will make it right. Thanks