Hi Norm , Ironbark and all,
If I get a spark problem ,I would try a new NGK or Bosch spark plug and if I still have a problem with the spark I would
change the coil.
If you think about it most mower coils can't last for ever with all the heat and vibration that they put up with ,most coils
are mounted over the hot cylinder instead of the crankcase end.
As we know.
There are a few things to check if your spark plugs are failing prematurely.
Repeated overheating of the spark plug tip can cause the plug to prematurely fail. Overheating can be caused by many things like pre-ignition and a malfunctioning cooling system. Pre-ignition can lead to heat building up in the combustion chamber causing the spark plugs to fail.
1 take notice if your mower starts to burn oil, as it can be an indicator that your spark plugs may be damaged prematurely
2 check for overheating ,blocked cooling system ,damaged fan or cowl.
3 Pre-ignition ,Black, dry soot on the electrodes and insulator tip indicates a carbon-fouled spark plug. This carbon buildup decreases the lifespan of a spark plug and can lead to hard starts, decreased acceleration, engine misfires ( check fuel mixtures and restricted intake side
or restricted exhaust side.
4 The gap between the spark plug’s center and side electrodes needs to be calibrated perfectly to ensure optimal engine performance. Having the right gap ensures that the arcing occurs at the proper voltage to ignite the fuel and generate the combustion that makes the engine run. If the gap isn’t set correctly, extra stress could be placed on the spark plug tip which could cause it to erode and wear out prematurely.
5 A faulty coil will have a plug that is not firing correctly and the plug will become fouled with fuel and oil pretty quickly because it never gets hot enough to burn off these deposits, you can hear sometimes when the plug or coil is faulty because the engine makes popping noises out the
exhaust.(like a slight misfire when you start to get a problem) (weak spark)
The fuel mixture can be incorrect if the needle and seat isn't working correctly or the fuel height in the carby is set to high or low.
Every mower I work on the cowl is removed and everything cleaned with compressed air so I know I won't get overheating
problems as I assume most of us do this .If you can hear the motor pinging and it's not a weak spark then you would need
to clean the carbon out of the motor if there are no other problems causing this.
low compression can cause misfiring as well as a damaged cam shaft .
Cheers
Max.
