Metering Valve Assembly: The photo below shows the metering valve assembly. This should operate smoothly and consistently. The metering valve is in the fork of the lever and goes down into the body of the carburetor. The lever is operated by the metering diaphragm.
To remove the assembly, you remove the screw that holds the shaft in place. Be careful not to loose the spring. It's not included with most kits. The round gray component in the image above is a 'Welch' plug.
If a carburetor is extremely gummed up, it may be necessary to clean out the idle ports. The only way to properly clean them is to break this plug out and clean the area behind it. You'll need a replacement so don't break the plug out if you don't have a replacement. If you think this area will be dirty, you can order a kit that includes the Welch plugs.
The orange arrow in the next photo shows you the port that allows the fuel to flow from the metering chamber to the high-speed jet. The red arrow points to the port that allows fuel to flow to the low-speed jet. The return spring for the metering lever can be difficult to work with, especially if you have big fingers. If you take a length of monofilament fishing line make a loop in it then insert it through the hole in the lever and then into the spring, the spring won't be so difficult to work with.
You can also insert the loop through the hole in the lever when disassembling the metering valve assembly to help the lever and spring together. Heavier line works a bit better because it doesn't pull out as easily. Line that's easier to see is easier to work with. This is 30lb test Red Lightnin' line by Zebco. Fuel Pump: The following image shows the fuel pump assembly.
THIS is what the carburetor looks like before removing the cover. The main component of the fuel pump is the diaphragm. It contains the reed valves that act as check valves to force the fuel to flow in one direction. The fuel pump is actuated by pulses of air from the engine crankcase. The port 'W' is where the carburetor mates to the port in the head. It's ported to 'X'. When the fuel pump cover is in place, it mates to the 'X' that you see on the cover. Air pulses pass to 'Y' through the fuel pump cover.
That causes the diaphragm to pulse which actuates the fuel pump reed valves. The fuel path is shown in red and progresses in order. The points with the same letter on the cover and on the body of the carburetor are mated when the cover is in place.
Note: The image above is a Flash graphic. You can right-click on it and select 'zoom in' from the dialog box. Drag the image with the left mouse button to navigate when zoomed in. This image has Dacron fishing line through all of the passages in the body of the carburetor to show you which ones are connected. All of these passages as well as the fuel filter must be clean and free of varnish. If any trash gets under either of the fuel pump reed valves, they will not function properly and the engine will not run.
High and Low Speed Jets: On some 2-cycle carburetors, you will have two adjustable jets. One is for high-speed operation and one is for low-speed idle operation. These are typically marked. Below, you can see the markings on the body of the carburetor. On some engines, the adjusters are different colors blue for low-speed, red for high-speed.
This is a generic replacement carburetor and has no slot in the jet shaft. This type of adjuster is designed to have a plastic cap pressed onto it. If you're replacing your old carburetor, you will need to transfer them from the old carburetor to the new one. If they are cracked, you will need to replace them. Adjusting the Carburetor: Adjusting the idle and high-speed jets. When adjusting these jets, you need to start with the idle jet.
Generally the manufacturer or other online sources give you the recommended starting point tighten until the needle touches the seat then back it out x number of turns. When you do this, don't use any significant force when closing the jet down. You can cut a groove in the needle and damage the seat. After getting the idle jet set so that it will idle smoothly or will at least run well enough so that it doesn't stall , you can move to the high-speed jet. You will increase the speed of the engine and adjust the jet.
Turn it one way then the other to get the smoothest operation. Continue doing this until the engine runs smoothly at the highest speed that it's designed to operate.
Running an engine lean can lead to destroying an engine. It may be counter-intuitive but restricting the fuel too much can cause the piston and head to run hotter than if there is too much fuel.
When you are at the point of being too rich or too lean, the engine will rev higher lean or begin to run rough rich. It's better to set the carburetor to be very slightly rich than slightly lean. Idle Speed Adjustment: As you get the idle jet adjusted, you may want to adjust the idle speed. The idle speed adjustment is much like it was on the 4-cycle carburetor.
It simply holds the throttle open slightly. The idle speeds isn't critical, generally. Flydat Operator's Manual. Flydat Control Operator's Manual. This website uses cookies to manage authentication, navigation, and other functions. By using our website, you agree that we can place these types of cookies on your device. View e-Privacy Directive Documents. Reconsider Cookies You have declined cookies. This decision can be reversed. July 1. Dec 1. Sep KB. FLYdat Manuals.
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