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Your mower with thermal engine remained in the garage this winter and refuses to start at the arrival of the spring? Do not panic! Do not bother on the launcher, look instead for the carburettor.

overhaul of a mower: carburettor with tank

Practical advice

To avoid "scrubbing", it is recommended to use a stabilizer (Briggs & Stratton) mixed with the fuel. One dose (a vial stopper) treats 5 liters of gasoline.
Gasoline 95 or 98 is denatured over time. Builders advise to always refuel with new gasoline unless it has been stabilized.

Most commonly branded Briggs & Stratton or Aspera-Tecumseh, the thermal engines of lawnmowers are equipped with two types of carburettor: diaphragm (see the "Change the membrane of a mower carburetor", System D No. 663) or tank. It is on this last model, the simplest, that our intervention takes place.
Indeed, if the engine refuses to restart after a long winter rest, more than the ignition, it is often the carburation that proves the cause of the "breakdown". For one simple reason: the stagnation of gasoline in the tank for several months forms deposits that can clog the sprinklers. This problem is called the "scrub". The solution remains a good revision. It requires the removal of the carburetor and a small hour of work.

Anatomy of the carburetor

The role of the carburettor is to ensure a homogeneous and precisely dosed air-fuel mixture; injected into the cylinder, it must maintain the internal combustion.

Tank

The tank contains the needle float which keeps the fuel level constant. It is related to the calibrated nozzle that sprays the gasoline in very fine droplets into the mixing chamber. There, a shutter called butterfly, actuated by the user, dose the flow of air-fuel mixture ensuring the engine power. A device called starter or "choke" makes this mixture richer to facilitate cold starts.

Mixing chamber

Placed under the tank, the mixing chamber, here horizontal, is more or less obstructed by the butterfly. Each of its ends terminates in a flange: connected to the intake pipe, one communicates with the engine cylinder; the other with the air filter. At the front of the chamber, some models include a priming pump.

The revision

● Before disassembling the tank, empty the tank and disconnect the hose. Disconnect the controls and the grounding stud from the ignition (which allows the engine to stop). Loosen and remove the two screws that secure the intake pipe to the cylinder. The entire carburetor can then be deposited.

● Unscrew the brass hollow screw under the tank. Its role is twofold: it maintains the tank and its calibrated hole on the side is the nozzle. On other models, the latter is embedded in a well but remains removable with a screwdriver. Clean the tank and blow into the orifice of the nozzle. Do not use steel wire that could change its gauge.

● Check the travel of the float and its valve regulating the arrival of gasoline. The float consists of two parts welded to tin; a small hole may form at their junction resulting in a risk of increasing the float. If so, change it or make a spot weld. When reassembling, replace the tank seal.

Install the tank carburettor on the crankcase

tank carburettor of a tensioner and its gas tank

The tank carburettor (left) is placed here on the casing of a mower equipped with a diaphragm carburetor which is one with the fuel tank.

Unplug the hose

disconnection of diurit

Unplug the candle and pull out the tank by pulling it upwards: its lugs slip into notches in the turbine housing.
Disconnect the hose by removing its clamping clips.

Remove the intake pipe

remove the intake pipe

From top to bottom: the air filter, the body and its priming pump, the tank.
The front intake pipe connects the carburetor body to the cylinder.
Remove the two screws.

Unplug the linkages

disconnection of linkages

With the air filter removed, unplug the gas throttle linkage and spring loaded linkage with a pair of pliers.
They are joined to the diet regulator.
Pull the lug out of the engine stop.

Clean the tank

Carburetor cleaning of a tensioner

Loosen and unscrew the hollow central screw which holds the tank and acts as lateral jet.
Clean the inside of the bowl with a brush and white spirit.
Wipe with paper.

Change the support gasket of the tank

change of seal on a tank

The vessel support shows the central well communicating with the mixing chamber.
By tilting the float, the needle can be removed from its seat.
Change the support gasket of the tank.

Unclog the nozzle

clean the nozzle of a tensioner

The nozzle is in the form of a small screw having a calibrated orifice.
To unclog it, use the blow gun.
When reassembling do not forget the seal of the screw.

Change the joints

change the worn joints of the intake pipe and the cylinder

A damaged seal causes air intakes that affect engine speed: changing the seal between the intake pipe and the cylinder and that of the flange that connects the pipe to the carburetor body.


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