.20
The spark plug gap for a Murray 12 hp riding lawn mower should be set at .020 inches. This is equal to .5 mm.
what spark plug do i need for a 3.75
0.030-0.035
0.028-0.030"
need the engine model, type and code
I am assuming that the mower doesn't start.... My first guess would be that you are not getting spark to ignite the gas in the engine. Check to see if you have spark at the spark plug.
The spark plug gap for a Murray 3.5 horsepower lawn mower should be set at .030 inches. A new spark plug will come with the gap preset and should need no further adjusting.
Should be 5/8
Spray some ether in the carb. If it fires, it has spark, but not getting fuel. start there.
Without knowing what engine or what kind of mower it is this is just a guess. But, it is possible that your flywheel and/or coil have gotten rusty and are not getting the conact that they need to make the spark. Try removing the cover and sanding the flywheel and coil. If it is a riding mower with a key switch there are many possibilities including anything from a bad switch to one of the safety switches.
RC12YC Champion
In order to replace the drive belt on a 42 inch cut Murray riding lawn motor, first remove the blade after disconnecting the spark plug. The drive belt is now exposed for easy replacement.