I have two pushmowers that I do not have owners manuals for nor do I know what type of service these should receive. I also have a Lesco weedwhip which I have the same question for. How do you know what the sparkplug gaps should be? I can pull out the old plugs and check what they were inside the machine, but without havign any books I do not know what the actual should be. On normal service do you just change sparkplugs once a year for the heck of it or is the manufacturers change recommendation really important. I am new to the mechanical world so please forgive my innocently probably simple questions.