How often should the spark plug be replaced on a lawnmower? I have a Craftsman 917.388834. B&S 4.5 engine. 21" cut

Ricness, February 2009

Every engine maintenance manual I have (literally thousands) states quite catagorically what the service interval is for the plug. In the case of your Briggs engine, (and indeed any Briggs engine less than 15 years old), it's every 100 hours of normal operation. That's 2 hours a week, every week for a year (ish). Obviously this will vary depending on the size of your lawn!

Assuming a 'carb-on-the-tank' model engine, replacng the carb diaphragm will probably cure your rough running, and the plug won't soot up. Cheap and easy fix.

phil_saunders@bigfoot.com

Phil Saunders, February 2009

Thanks Cledlyn, I took out the plug and it was very black. I cleaned it off with wire brush and reinstalled. Mower still sounds weird. As if it's trying to die but struggling to stay alive.

Ricness, February 2009

There is no real service interval for lawnmowers is the simple answer! The best answer would be to remove, clean and regap the plug every year before you start using it. Correct setting should be in the handbook or on the Briggs and Stratton website. If the mower becomes hard to start or cuts out / loses power, then replacing the plug is a good and cheap place to start - if it's not the plug, It will do no harm changing it anyway.

Cuckoo999, February 2009

Spark plugs last 10,000 miles in a car but in a lawnmower the problem is they tend to soot up and become contaminated with oil deposites. They should last at least 5 years but they should be cleaned and checked at the pre-season service

cledlyn, February 2009