Owners of outboard motors Johnson They know that their boat's heart beats exactly as long as the mixing system is working. carburetor It is responsible for preparing the right fuel-air mixture, on which power, efficiency and stability of the engine depend, and any deviations in its operation instantly affect the propeller traction and gasoline consumption.
Start-up problems or floating speeds often scare beginners, but most of the time, it's just plain pollution or adjustment. Understanding how this unit works will help you avoid expensive repairs in the workshop. fuel-system It extends the life of the motor for years.
In this article, we will analyze in detail the design of carburetors installed on motors. Johnson You'll learn how to diagnose faults correctly, what tools you'll need to set up, and how to avoid common assembly errors, and attention to detail is the most important thing.
Design and operation of Johnson carburetors
Most of the two-stroke engines JohnsonAnd especially in the late twentieth century, they were equipped with membrane-type carburetors, and their key feature is their independence from gravity, which allows the motor to operate even when the boat is rolling. fuel-pumpbuilt into the housing, which pumps gasoline due to the pressure drop in the crank chamber.
The mixing process takes place in a diffuser, where the airflow creates a dilution. jellyThe vents are highly calibrated by the plant, and the disruption of the throughput of these holes leads to impoverishment or enrichment of the mixture, and the pressure regulator membrane is another critical node.
It's worth noting that the design can vary depending on the power. carburetorAnd there may be two or three of them on more powerful V-engines, and synchronizing them is the key to smooth thrust in all modes.
The difference between Johnson carburetors and Tohatsu and Mikuni
Johnson carburetors often have a specific float chamber shape and a unique arrangement of adjustment screws, which requires a personalized approach when searching for parts.
Typical malfunctions and methods of their diagnosis
The first sign of problems with the carburetor is usually unstable idling, the engine may stop when the gas is discharged or, conversely, do not regrow. air-breath Or clogging up the idle channels, and the diagnostics start with a visual inspection.
If the engine "troit" or loses power at high revs, most likely, clogged chief-jeckel It's also worth checking the condition of the fuel filter-sludge, which is often installed in front of the carburetor, and the water in gasoline is the main enemy of membrane systems.
⚠️ Warning: Before any work with the fuel system, be sure to close the fuel crane and disconnect the supply hose. Gasoline vapors are flammable, and spilled fuel can damage the boat's coating.
Accurate diagnosis often requires removal of the node. gasket And the drying of these rings causes leakage that you can't compensate for with the screws, and you can use an aerosol cleaner to check the channel capacity.
Tools and preparation for maintenance
You can't have a good repair without the right tools. Johnson You're going to need a set of screwdrivers, including little screw screws for adjusting screws. spray-cleaner A carburetor that dissolves resinous deposits.
Make sure to prepare a repair kit, the so-called Rebuild KitIt includes all the necessary membranes, gaskets, needle valve and often new jellyplates, and the use of old rubber parts after disassembly is strongly discouraged, as they lose elasticity.
The workplace should be well lit and protected from the wind. Small parts are easy to lose, so use a magnetic tray or container with cells. Cleanliness when assembled is the key to success, one grain of sand can disrupt the entire assembly.
☑️ Preparation for carburettor repair
Process of disassembling and cleaning knots
Disassembly begins with removing the air filter and disengaging the throttle throttle, carefully unscrew the mount nuts and remove the carburetor from the engine. When disassembling, record the sequence of the parts removed, the best thing is to take a photo at each stage, which will help with the reverse assembly.
After dismantling, disassemble the knot into its components, and thoroughly blow all metal parts, jelly and channels with a cleaner. Pressure-air purging It is mandatory for all holes, even if they appear clean. Do not use metal wires to clean the jellyclera, so as not to change their caliber.
Pay special attention to the float chamber. The bottom often accumulates dirt and oxides that need to be removed. Check the ease of travel of the float and the needle valve. If there are signs of wear or risks on the needle, replace it with the valve saddle.
| Element | Sign of malfunction | Method of recovery |
|---|---|---|
| Pump membrane | Cracks, petrification | Replacement (included in the remake) |
| jiclair | Pollution, scoop. | Washing and purging |
| Needle valve | Wear of the needle cone | Replacement of a needle-saddle pair |
| Throttle axis | Luft, snacking. | Lubrication or replacement of the knot |
Adjustment of the carburetor: screws L and H
The assembly is complete, and now the most important step is the adjustment. Johnson There are usually two main adjusting screws, marked with letters. L (Low) and H The L screw is responsible for low engine speed and transients, and the H screw is responsible for maximum power.
The initial setup is done by turning the screws to the point (no fanaticism!) and then turning them to the standard number of revolutions specified in the manual (usually 1-1.5 revolutions). After starting the engine, let it warm up. The L screw is adjusted on the heated engine at idle.
When adjusting the screws, use a rev counter (tachometer) connected to a candle wire. It is difficult to determine the optimal idling speeds by hearing, and exceeding the limit can damage the lower unit.
When rotating the L, achieve the most stable and high idle speeds. Then, with the throttle stop screw, reduce them to normal (usually 900-1000 rpm). The H screw is adjustable under load or on water, but the initial setting can be done by hearing, looking for peak revs when the throttle is sharply opened.
Synchronization of carburetors on multi-cylinder engines
If you Johnson It has two or more carburetors, and they have to be perfectly synchronized, and it causes one of the cylinders to overheat and lose power. throttle-plate.
The process is to align the opening of the valves on all the carburetors at the same time, first adjust the base position of the gas cable, then use the synchronization screws to achieve the same dilution or mechanical position of the valves, which requires patience and accuracy.
⚠️ Warning: Incorrect synchronization can lead to detonation and destruction of the piston group. If you are not confident in your abilities, it is better to entrust this procedure to professionals with the appropriate equipment.
After mechanical synchronization, be sure to check the engine under load. The engine should respond to the gas instantly, without dips and jerks. The smooth sound of the exhaust is the best indicator of the correct setting. fuel-system.
The quality of gasoline directly affects the life of the carburetor: use only fresh fuel with the octane number recommended by the manufacturer, and add a stabilizer for long-term storage.
Prevention and seasonal storage
So next spring, you don't have to spend the weekend repairing, you can properly mothball the engine, and the main task is to remove all the gasoline from the carburetor, and the remaining fuel evaporates, leaving a resinous plaque that clogs. jelly It damages the membranes.
The best way to conserve is to generate fuel from the float chambers, so you can shut off the faucet and let the engine run until it stops. Alternatively, use a fuel stabilizer if you plan to keep a boat full of tank, but the carburetor is still better to drain.
Regularly replacing fuel filters and using a quality blend of oil and gasoline will significantly reduce the risk of failure. carburetor It is a precise tool that requires pure “nutrition.”
How often should I clean the Johnson engine?
Preventive cleaning is recommended every 2-3 seasons of active operation or when the first signs of unstable operation appear.
Can I wash the carburetor with ultrasound?
Yes, an ultrasonic bath effectively removes deposits, but before that you need to remove all rubber and plastic parts. Metal parts (body, jelly) tolerate cleaning perfectly.
Why does the engine stop when the gas is opened?
This is a classic sign of misconfiguring transition modes or clogging of the idle jellier, and the problem may be the accelerator pump, if it is designed.