Briggs & Stratton 725EXi, 163cc (model 104M)
The 725EXi is Briggs & Stratton's 163cc overhead-valve push mower engine. Its model number starts with 104M. You will find it on 21 and 22 inch self-propelled mowers from Toro, Craftsman and others.
Model 104M163cc OHVVertical shaftReadyStart
Specs and part numbers at a glance
- Model number starts
- 104MSold as the 725EXi in the US and the 675EXi in Europe.
- Displacement
- 163 cc (9.93 cu in)
- Bore x stroke
- 2.688 in x 1.75 in
- Spark plug
- Briggs 594056 (resistor)The parts list for 104M02-0001-F1 gives 594056. The operator's manual lists 491055S for 100000-series engines. Use the number your own parts list shows.
- Plug gap
- 0.030 in (0.76 mm)
- Plug torque
- 180 lb-in (20 Nm)
- Oil
- 15 oz (0.44 L), SAE 30 or 10W-30EXi engines use Just Check & Add: Briggs says no oil changes are needed, only top-ups. You can still change it.
- Air filter
- Paper cartridge 593260 with foam pre-cleaner 595191
- Fuel
- Fresh unleaded, 87 octane or higher, no more than 10% ethanol (E10). Do not use E15 or E85.
- Coil (armature) air gap
- 0.006–0.014 in (0.15–0.35 mm)
- Valve clearance
- 0.004–0.008 in (0.10–0.20 mm)Leave this to a dealer unless you have done it before.
Find the model number
Briggs & Stratton stamps the model, type and code into the metal of the engine, in one of three places (A, B or C on the drawing below): above the spark plug, on a plate between the valve cover and the air filter, or above the muffler. On this engine the model starts with 104M. The full number looks like 104M02-0001-F1: model, type, then trim. If you only find 9 characters, add a zero to the front. The code is the build date (year, month, day) and decides which carburetor kit fits.
Where the number is stamped
- ABriggs & Stratton: stamped into the metal just above the spark plug. You may need a flashlight.
- BBriggs & Stratton: stamped on a small metal plate between the valve cover and the air filter.
- CBriggs & Stratton: stamped on the sheet metal above the muffler, which can be on either side.
- DHonda: the model (it starts with G, like GCV170) is on a sticker on the engine. The serial number and type code are stamped into the side of the engine.
Mowers that use this engine
These mowers are listed by their makers with a Briggs & Stratton 163cc engine. Check the stamped number on your own engine before you order parts, because makers change engines between years.
| Mower | Model no. | What the maker lists |
|---|---|---|
| Toro 22 in. Recycler with Personal Pace | 21462 | Toro lists a Briggs & Stratton EXi 163cc engine |
| Craftsman M125 21 in. push mower | CMXGMAM7815145 | Craftsman lists a 163cc OHV Briggs & Stratton engine (series not stated) |
Parts and part numbers
Check the number against the parts list for your exact model before you order.
| Part | Part number | Notes |
|---|---|---|
| Spark plug (resistor) | 594056 | From parts list 104M02-0001-F1, ref 337 |
| Spark plug wrench | 19576S | Ref 383 |
| Air filter cartridge | 593260 | Ref 445 |
| Foam pre-cleaner | 595191 | Ref 535A |
| Carburetor overhaul kit | 594636 or 590589 | 594636 for code dates after 15030800; 590589 before 15030900 |
| Float bowl gasket (pack of 5) | 594633 or 593235 | 594633 after code 15030800; 593235 before |
| Float bowl | 594632 | After code 15030800 |
| Main jet (standard) | 594060 | High-altitude jet is 594063 |
| Fuel line | 791766 | Ref 187 |
| Starter rope | 591108 | Ref 58 |
| Dipstick | 796503 | Ref 523 |
Tools you need
- Spark plug socket or Briggs wrench 19576S
- Wire-type gap gauge
- Torque wrench (lb-in range)
- Screwdriver and 3/8 in. drive socket set
- Oil drain pan
- Carburetor cleaner spray
- Gloves and eye protection
Maintenance and repairs, step by step
Replace the spark plug
Once a year, or sooner if the engine is hard to start.
| 01 | Pull the boot straight off the plug. Clean around the plug so dirt does not fall into the cylinder. | Engine cold. |
| 02 | Remove the plug with a spark plug socket or the Briggs plug wrench 19576S. | |
| 03 | Set the gap on the new plug to 0.030 in (0.76 mm) with a wire gauge. | Check, don't assume: new plugs are not always gapped right. |
| 04 | Thread the plug in by hand first so it can't cross-thread. | |
| 05 | Tighten to 180 lb-in (20 Nm). Push the boot on until it clicks. | Torque from the Briggs operator's manual. |
Service the air filter
Every 25 hours or once a season; more often in dust.
| 01 | Press the tab and lift off the air filter cover. | |
| 02 | Lift out the paper cartridge and the foam pre-cleaner. | |
| 03 | Tap the cartridge gently on a hard surface. Replace it if it is torn, oily or you can't see light through it. | Cartridge 593260. |
| 04 | Wash the foam pre-cleaner in soapy water, rinse, and let it dry completely. | Pre-cleaner 595191. |
| 05 | Refit both and close the cover until it latches. |
Change the oil
After the first 5 hours on a new engine, then every 50 hours or once a year.
| 01 | Run the engine a few minutes to warm the oil, then stop it and pull the plug boot. | |
| 02 | Drain or siphon the tank first if you can. Tip the mower onto its side with the air filter facing up, and let the oil run out of the fill tube into a pan. | Air filter up, every time. Tipping it the other way floods the filter with oil and fuel. |
| 03 | Set the mower level. Pour in about three quarters of 15 oz (0.44 L) of fresh oil, wait 3 minutes, and check the dipstick. | SAE 30 or 10W-30, API SJ or higher. |
| 04 | Add a little at a time until the oil reaches the full mark. Do not overfill. | |
| 05 | Refit the dipstick and take the old oil to a recycling point. |
Clean the float bowl and main jet
When the engine won't start or dies after fresh fuel and a new plug.
Safety Work outdoors on a cold engine. Gasoline vapor ignites easily, so no smoking, sparks or pilot lights nearby, and wipe up spills before you start the engine.
| 01 | Turn off fuel supply if your mower has a shutoff. Otherwise run the tank dry or drain it. | |
| 02 | Remove the air filter cover and filter so you can see the carburetor. | Take a photo of the linkage and springs before you touch anything. |
| 03 | Put a rag under the carburetor and remove the bowl screw. Lower the float bowl off. | The bowl gasket is 594633 (or 593235). |
| 04 | Spray carburetor cleaner through the main jet and the bowl screw passage. Clean out any varnish or water in the bowl. | Never push wire through the jet; it enlarges the hole. |
| 05 | Check that the float moves freely and the needle is clean. | If parts are worn or the gasket is hard, fit the overhaul kit 594636 (or 590589 before code 15030900). |
| 06 | Refit the bowl with the gasket seated, then the filter. Refill with fresh fuel and test. | Do not bend the governor linkage or move the governor spring. |
Troubleshooting by symptom
| Symptom | Likely cause | What to do |
|---|---|---|
| Won't start after storage | Stale fuel in the tank and carburetor | Drain the tank, refill with fresh fuel. If it still won't start, clean the float bowl (see the carburetor job). |
| Starts, then dies | Varnish in the carburetor main jet, or a blocked fuel cap vent | Clean the float bowl and main jet. If it only runs with the fuel cap loosened, replace the cap. |
| Hard to pull, then won't turn | Blade hitting grass or debris, or a bent blade | Disconnect the plug wire, tip the mower air filter side up, clear the deck and check the blade. |
| Surges or hunts at full speed | Dirty air filter or a partly blocked jet | Replace the filter, then clean the carburetor. Do not adjust the governor spring or linkage. |
| Blue or white smoke | Mower was tipped the wrong way, or oil overfilled | Check the dipstick. Always tip a Briggs push mower with the air filter side up. |
| No spark | Fouled plug or wrong coil air gap | Fit a new plug at the correct gap. Check the coil air gap with a gauge card. |
Owner's manuals and parts lookups
These go to the maker's own sites.
- Briggs & Stratton manual and parts list lookup Enter the full model-type-trim number
- Briggs & Stratton: where to find the model number Push mower engines
- Briggs & Stratton model numbering key (PDF) What each digit means
- Briggs & Stratton EXi series specifications 625EXi, 725EXi, 875EXi
Something wrong or missing?
Tell us the full model number on your engine and what you found.