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EX Module 2
Transcript of EX Module 2
The Subaru EX engine is equipped with a horizontal draft, bowl type carburetors.
Main system feeds fuel to the engine at medium and high speed operation. Fuel is metered by the main jet and flows into the main nozzle. Air measured by the main air jet is mixed with the fuel through the bleed holes of the main nozzle. The fuel/air mixture is fed into the venturi and mixed once again with air from the air cleaner. This fuel/air mixture is now of optimum concentration and is fed into the combustion chamber of the engine.
Choke system is used for easier start of a cold engine. When the engine is started with a closed choke, a vacuum is created as the piston moves downward in the cylinder. This vacuum draws more fuel into the venturi. The reduction in the amount of air coupled with the increase in the amount of fuel will change the air-to-fuel ratio. This richer fuel mixture makes it easier to start the engine.
Diagnose the problem
Check the spark plug. Examine the color of a spark plug. A light tan to gray color indicated normal fuel delivery and normal engine conditions. Whitish gray hue on the plug’s insulator signifies lack of fuel.
Check the exhaust. After a warm up time of three to five minutes, the engine’s exhaust should be free of any smoke. Blue gray smoke suggests that the engine is burning too much oil; black smoke indicates that the fuel mixture is too rich.
Finally, the carburetor is the last item to check.
If an engine seems to be running too rich, check the air cleaner first. A restricted air cleaner will cause reduced air flow creating a rich fuel mixture. To troubleshoot, remove the air cleaner and clean out its housing. If the filter element is dirty, clean it or replace it with a new one. Run the engine for a few minutes and see if the exhaust cleared up.
Remove the main jet with a flat head screwdriver and use pliers to pull it out, if required.
This vent allows fuel and air to flow during idle and low speed operation.
Remove the float.
12 or 13mm box wrench or socket
needle nose pliers
10 mm socket
Find a light source and look through it to see if there’s any dirt there. If dirty, use a very thin wire to clear heavy debris from the main jet.
Throat of a carburetor
Using a 10mm wrench on the flats of the plastic fuel valve bowl, remove bowl and inspect for fuel residue buildup.
Remove the carburetor bowl with 12mm wrench and bowl gasket (must remove gasket
before using carb cleaner)
Spray carb cleaner into the fuel valve to clean debris from valve and float valve.
Inspect float valve movement by gently moving the float.
Spray carb cleaner through the main jet.
Spray carb cleaner up the main nozzle.
Reassemble fuel valve bowl back into fuel valve assembly: do not over tighten.
Re-install carburetor bowl gasket. Check for proper gasket placement.
Reassemble the carburetor bowl.
Note the position of the fuel drain plug on the carburetor float bowl under the
Typical Carburetor and It's Parts
Gasket Chamber- Seal/Packing
Float Sub Assy
Float Chamber Sub Assy
Pin Float Lever
Needle Valve Assy
Low Speed Screw
There are some differences in carburetors
EX 13, 17, 21
Notice that the carburetor on the right has a main nozzle that is removable. The nozzle inside the carburetor on the left is not visible and therefore may not be removed or serviced; however, it may be cleaned.
EX 35 and EX 40 have some parts that are different from the other two carburetors.
Screws for Cable Choke
Choke Shaft Sealers- not serviced?
Idle Mixture Screw- not serviced
Parts of Solenoid
The carburetor mixture settings are factory pre-set for optimum all-round engine performance and to satisfy stringent EPA regulations.
Various components in the carburetors such as jets and choke configurations can vary between engine specifications due to air filter types and applications.
understand the basic structure of the carburetor
understand how the carburetor functions
know how to diagnose a carburetor problem
1. Check to see if there is gas in the bowl by loosening or removing bowl drain screw. Also look for signs of water in gasoline.
2. Turn off gas by the fuel valve
3. Loosen the fuel bowl bolt
Clean the inside of the carburetor bowl with carburetor cleaner.
Wash the parts. Use an ultrasonic cleaner and make sure all the parts are dry before reassembling the carburetor if necessary.
The float chamber or carburetor bowl is located below the carburetor body.
Through the operation of the float and the needle valve, the float chamber maintains a constant fuel level.
Gravity causes fuel to flow from the tank to the carburetor inlet, through the needle and seat and into the float chamber.
As the fuel level rises, the buoyancy of the float causes fuel to rise until it reaches the desired level. At this point the needle valve shuts off the fuel flow.
As fuel is consumed by the engine, more fuel enters the float chamber as the float drops to maintain the desired level.
Fuel system problems are common in small engines, possibly being the cause of a "won't start" condition.
Inspection of various components of an engine can lead to the source of these problems.
Check engine compression. Slowly turning an engine over with the recoil starter rope can sometimes give you an idea if the engine has adequate compression. The use of a compression tester is a better indicator, if available.
Minimum compression for most engines to run is in the range between 40 to 60 p.s.i. If compression is low, look for problems with the engine's valves, rings or cylinder walls.
Another cause of a rich running condition is the choke.
check to ensure that the choke valve in the carburetor is fully open when the control lever is in the run position.
adjustments or repairs to the choke controls and/or cables may be necessary
In a "won't start" situation, you can confirm a fuel delivery problem by manually "priming" the engine.
Squirt gasoline or carburetor cleaner directly into the throat of the carburetor, then attempt to start the engine. If the engine fires but then dies out, it most likely is running only on the fuel you primed it with but it will not pick up fuel on its own.
If the engine does not fire, the problems may be somewhere other than in the fuel system.
Remove the air cleaner assembly
This can be done without removing carb from engine.
Be careful not to damage jet or enlarge the orifice!
Remove the pilot jet from the top of the carburetor.
A clogged jet will cause the engine to surge.
Again use a thin wire to put through the middle opening all the way in, make sure it is open.
If the main jet is partially clogged, the engine will run lean. May need to run the engine with the choke partially closed to get it to run smoothly.
EX 13, 17, 21
provide a simulation of removing the cleaner assembly?
Need to make sure if serviced?
short video how to check engine compression
picture of fully open choke
picture of a carburetor on the engine with an arrow pointing to it
This module will focus on the carburetor and it's parts. It will go through its functions and basic troubleshooting.
Pilot system supplies fuel to the engine during idling and low speed operation.
Fuel is initially metered by the main jet and then metered once again by the pilot jet.
At the pilot jet, the fuel is mixed with air measured by the pilot air jet and then the fuel/air mixture is fed to the engine through the pilot outlet and the bypass.
During idling, fuel is fed to the engine mainly through the pilot outlet.
Which engine(s) do you think this carburetor belongs to?
This carburetor is bigger than the other two, therefore it belongs to a bigger engine.
The bowl of the smaller engine is more flat than the bowl of engine EX27.
The stepped bottom of the bowl is a signature look for this engine.
Below are two videos that further explain the carburetor and its functions.
Float Carburetor Outer Part
Float Carburetor Inner Part
Here's a video summarizing how to clean a carburetor.
Carburetor float bowl has a drain screw. You can remove the drain screw from the carburetor float bowl to see if fuel is getting to carburetor float bowl. Turn on the fuel valve, open the carburetor drain screw and check to see if fuel bowl has fuel in it. If fuel does not leak out of the drain screw, then you know the problem is in fuel needle, fuel tank, on-off valve, the fuel filters in the shutoff or fuel tank. If fuel does leak out, then the problem is most likely in the main jet or pilot jet.