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Set the gap to 0.020-0.030 in (0.5-0.76 mm). Measured gap and size specs for Briggs, Honda, Kohler, Kawasaki and Craftsman engines, plus socket sizes.

Tested 5 lawn mower spark plug testers on 4 engines in spring 2026. See the $6 inline pick that wins, which to skip, and how to use one in 60 seconds.

Check the plug, not the mower. Most lawn mower spark plugs take a 5/8-inch (16 mm) or 13/16-inch (21 mm) socket. Size chart by engine, plus 5 tested picks.

Clean a fouled mower spark plug in 10 minutes: wire brush the carbon, solvent the rest, re-gap to .030 in. Plus when the plug is past saving.

Test a lawn mower spark plug three ways in under 10 minutes: the ground-and-pull spark check, an inline tester, and the ohm test that misleads most owners.

Compare foam vs paper before you buy: which engines need foam, whether you must oil it, cut-to-size sizing, and how long a foam filter really lasts.

Replace a lawn mower air filter in 4 minutes. Get the 7-step swap, the orientation photo trick, and the real replace interval for your engine.

Skip the tune-up: electric mowers have no spark plug, air filter or oil. Here are the 4 jobs that matter, with intervals, costs and a gas-vs-electric table.

Tap the paper cartridge, wash the foam pre-cleaner, and check the oiling rule for your model year. Covers 100, D, E, L, S and X Series riders.

Swap your John Deere spark plug in 15 minutes: a 5/8″ socket, a .030″ gap, and why V-twin riders have two plugs - plus how often to replace it.

Find the right John Deere spark plug by model: M78543 (RC12YC), the NGK/Champion cross-reference, the .030 gap, socket size, and why V-twins take two.

Match your John Deere riding mower air filter by model: MIU14395 fits most 100-series; GY-series covers L/LA V-twins. Read your tag, pick OEM or aftermarket.

Tune up your John Deere in 5 steps — oil, air, fuel, plug(s), blade. Match the right LG kit to your model and skip the $100–$350 dealer bill.

Match the right Craftsman tune-up kit to your 917 model and engine. See genuine vs aftermarket value, what's inside each kit, and where to buy.