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After a long winter, when the lawn mower refuses to start, you do not have to fight on the launcher! If the fuel supply is out of the question and the new spark plug, the failure is surely related to a carburetor problem.

Lawn mower

  • Failures that occur on a machine stored for several months are often related to the presence of stagnant gasoline in the carburetor. It damages sprinklers and small ducts of tank carburettors.
  • In our example, the mower (Wolf Tools) has a 4-stroke engine (Briggs & Stratton) equipped with a membrane carburetor. It differs from the more traditional tank, by the absence of jet and float. It's a thin rubber membrane, taken between the upper part of the tank and the carburetor base, which adjusts the fuel intake by valve. After several years, this membrane deforms, hardens and pierces itselfso you have to replace it.

A simple and careful intervention

  • The membrane is clamped between two plates: the top of the aluminum tank is a bit special since it is rectified to give a good reach to the sole that forms the base of the carburetor.
  • A row of screws ensures the tightness of the membrane and its tightness. The carburetor body is equipped with two dip tubes ending with very fine filters that can be partially or completely closed by deposits.
  • Briggs & Stratton markets a complete kit including a diaphragm and its return spring. It is available from after-sales service centers, but also from repairers and garden equipment rental companies (take references from the engine).

What kind of fuel?

  • TheAbsence of additif in unleaded fuel reduces its life (lead was a preservative). As a result, gasoline stored for more than two months in a partially filled or improperly closed canister suffers the effects of condensation; the water contained in the can is not absorbed, mixed with the gasoline and makes it unusable (see box).
  • Since 2009, the SP95 gasoline is replaced by the SP95-E10, which includes 10% ethanol. This "biofuel" is incompatible with small petrol engines of lawnmowers, brushcutters, chainsaws... which can only use SP95 or SP98.

Repair in 7 key steps

repair kit

The repair kit (here Briggs & Stratton) includes a thin rubber membrane, very resistant, suitable for this type of carburetor and a spring return coil.

clean the filter

  • To access the carburetor, first remove the air filter by removing the central screw.
  • Clean with gasoline, then remove the bonnet (right).

disassemble the mower

  • Continue disassembly by removing the screws that secure the carburetor flange to the ground base of the fuel tank.
  • The membrane is pinched between these two parts.

remove the carburetor

  • The connection between the outlet of the carburettor and the engine intake pipe is by interlocking.
  • Simply pull on the carburetor body to pull it out.

clean the end filters

  • Flip the body to reveal the black membrane and the dip tubes.
  • End filters are easily closed.
  • Clean them with a brush with brass strands.

uncouple the control pull tab

  • After removing the small hood on one side of the carburettor, uncouple the control pulling the membrane to the air damper (located under the air filter) to the screwdriver.

plug in the new box

  • Equip the new diaphragm with the control puller and its return spring (supplied).
  • Engage the rod in a hole provided for this purpose.
  • Reconnect at the housing.

finish reassembly of the carburettor

  • Engage the carburetor in the engine intake pipe.
  • Fit the dip tubes into the wells of the tank.
  • Tighten the diaphragm screws and finish reassembly.

Tips for DIYers

• Avoid using fuel from the previous season and stored without additives. Indeed, to conserve fuel during winter periods, it is necessary to add a gasoline stabilizer (Bardhal, Briggs & Stratton, Motorex...), to buy from the repairer. This additive
incorporated allows trouble-free recirculation and protects the entire system against corrosion.
• At the end of the mowing season, drain the tank and carburetor completely. Run the engine until the machine is out of order and stops.


Video Instruction: How to Fix a Lawn Mower Carburetor