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Briggs & Stratton Spark Plug Gap Chart: .030 vs .020 and the Quantum Exceptions

Updated 2026-10-29 · Written and checked by the Manual Matters team against the manufacturer documents listed under Sources.

Short answer: Briggs & Stratton says most of its small-engine spark plugs are gapped at .030 inch. The main exceptions are certain Quantum engines and certain resistor plugs that use .020 inch, and platinum, iridium or twin-tip plugs, which Briggs says should not be regapped at all. Find your engine's model, type and code numbers before deciding.

Briggs & Stratton spark plug gap chart listing .030 and .020 inch gaps by plug part and engine
Briggs & Stratton spark plug gap chart listing .030 and .020 inch gaps by plug part and engine

Briggs & Stratton gap exceptions (from Briggs's own FAQ)

Plug (Briggs part)EngineGap
Most standard Briggs plugsMost small engines.030 in
RJ19LMC (591868)Quantum engines with code date after 110630x.020 in
RJ19LMC (591868)Quantum engines with code date before 110701xx.030 in
RJ2YLE (799876)Quantum 625, 675, 725 engines with code date after 110701xx.020 in
Resistor plug 692051General listing.020 in
Resistor plug 692051Vanguard engine models 050032 and 086400.030 in
Platinum, iridium, twin-tipAnyDo not regap

How to find your engine code date

The model, type and code numbers are stamped or labeled on the engine itself; your operator's manual shows where on your engine. The code is the date-based number the table above refers to. If you cannot find it, use the plug and gap your manual lists.

How to gap a plug

  1. Disconnect the spark plug wire and let the engine cool.
  2. Remove the plug with a spark plug socket.
  3. Confirm the replacement plug matches the part number in your manual.
  4. Use a gap gauge to measure between the center and side electrodes.
  5. If needed, gently bend the side electrode to reach the specified gap. Never pry against the center electrode.
  6. Skip steps 4–5 for platinum, iridium or twin-tip plugs.
  7. Thread the plug in by hand first, tighten with the socket, and reconnect the wire.

Not a Briggs?

Other brands use different gaps. Honda's GCV170/GCV200 manual specifies 0.028–0.030 in (Honda GCV guide), and Generac's GP2500i manual specifies 0.024–0.028 in (Generac GP2500i guide).

Briggs schedules spark plug replacement once a year; see the Briggs maintenance schedule.

Sketch of a spark plug showing the gap between the center electrode and the ground strap
Sketch of a spark plug showing the gap between the center electrode and the ground strap

FAQ

What is the spark plug gap on a Briggs & Stratton lawn mower?

For most Briggs engines, .030 inch. Some Quantum engines and some resistor plugs use .020 inch, so check the table and your engine code.

Should I regap a new iridium plug?

No. Briggs says platinum, iridium and twin-tip plugs should not be regapped.

Will a wrong gap stop the engine from starting?

Briggs lists the spark plug as one of the first things to check when a mower won't start. A plug with the wrong gap, a fouled tip or a loose wire is worth ruling out early.

Sources