Kiss stuff first - has he done simple engine maintenance (oil/filter change, air filter element clean/replace, drain old fuel) ?

Beyond that, he can get the mower's full model number from the cavity under the tilting seat and use it to possibly download a free manual from sears that may help.

Along with above first thing I would suspect would be carb. leaning out from tarnish/Gum. As sugested remove all the old gas, put some fresh with fuel additive. IF that don't work buy can of GUMOUT spray carb. cleaner and follow the instructions on can. Maybe you will get lucky without having to do carb. disassemble and clean-up.

Without knowing which engine, one can only give vague advice.
IF it's an older tractor, it may have an adjustable jet or not.
Post the Sears 917.xxxxxx number.

Personally, I'd probably put a good dose of carb cleaner IN THE FRESH FUEL where it'll actually go THROUGH the carb passages.
Also check for vacuum leaks.

This is a brand new mower. He just bought it. He would like to have some kind of an idea what it may be before he calls the service dept.

Well! IF it new then it's got to be carb. adjustment (too lean), Faulty carb. Spark plugs or ignition system faulty. Really unless your willing to tamper with it and void the warranty I would just call dealer. Any malfuncting NEW equipment dealer needs to deal with it.

"Well! IF it new then it's got to be carb. adjustment (too lean), Faulty carb. Spark plugs or ignition system faulty. Really unless your willing to tamper with it and void the warranty I would just call dealer. Any malfuncting NEW equipment dealer needs to deal with it".

This is exactly what I told him. Thanks for the replies.