I have a John Deere lawn tractor. I religiously change the oil and perform the lubrication per the recommended service intervals. I am wondering how critical it is to change the other things as regularly as recommended, including the air filter, fuel filter, spark plugs. Does this cost me horsepower, engine life, gas consumption?

 

They only need changing when they need it. I've seen some engines not need a fuel or air filter or spark plug for 5 year or more. Conditions are everything. It takes a car 30,000 to 40,000 miles to wear out a set of spark plugs. In a properly running small engine, imagine how long it takes to accumulate that kind of run time. An air filter stopped up can create some fuel economy problems and performance problems. If it gets full of dirt and wont tap out when you try to clean it, replace it. The fuel filter may last the life of the mower. It is good practice to replace it once in a while though, just to keep things from happening. Once every 3 or 4 years should be fine unless you don't keep your gas in a very clean container or conditions. The fuel and air filters and spark plug don't really affect engine life unless the air filter gets damaged enough to allow dirt to get through or bypass it. Changing your oil is your friend when it comes to improving engine life.

 

Totaly depends on number of hours used with the exception of the oil.
Oil need to be change at least once a year.

 

I wouldn't get caught up in watching hours. You might need a new air filter in 20 hours if conditions are really dusty and dry, or you might not need one in 500 hours if you have lush thick grass and a sprinkler system and non-dusty conditions. For that stuff, hours don't matter. Oil is the one thing out of all of them that I would base on hours more than the others. 50 hours on the oil is pretty much a baseline to work from. Less if conditions are hotter, dustier, etc... Once a year is normal for most homeowners with normal yards. If in a year, you hit more than 50 hours, you need to change it again.