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Here is an old gem. Print it out and keep it in your flight box.

Carburetor Basics by BOB GILBERT as appeared in Model Airplane News

<hr size="5" color="#0000ff" />

SET-UP AND OPERATION I'm an old-timer in the hobby, and my motto is "Keep 'em flying." Toward that end, I'll try to help you keep those engines purring! As simple as possible, this guide will enable you to properly set up 90 percent of the carburetors available today. I'll address 2-stroke sport-type engines up to .65 displacement that don't have tuned pipes, pumps, or three-needle valve carbs. THROTTLE? CHECK! FUEL? CHECK! ... To start, set the throttle linkage. If your throttle servo doesn't have an adjustable arm, get one. It will help you immensely when you make these adjustments. (This won't be necessary with newer radios that have servo-travel adjustment built in.) With the linkage disconnected, hold the throttle arm so that you can rotate the barrel toward the closed position. Rotate the idle-speed stop screw so that the barrel closes fully, then rotate it half a turn more. Don't back the screw out any farther, because on some engines this screw also holds the throttle barrel in place. If there's a locknut on the screw, tighten it. Now connect the throttle linkage to the servo, and adjust it so that the with the stick and trim fully down (emergency cutoff position) the barrel is completely closed, and with the stick and trim fully up (full throttle) the barrel will be 100 percent open. For idle, set the trim at the position that will open the throttle barrel 1/32 of an inch (about the size of a round toothpick at its thickest point) when the stick is fully down and the trim is fully up (idle position). Next, check the fuel system. The spraybar/needle-valve assembly should be positioned (relative to the tank) no less than a third, but no more than halfway, down from the top of the tank. The fuel tank will be pressurized with muffler pressure. Inspect all fuel lines, metal and otherwise, for kinks and splits. Look inside the tank unless it's brand new. Fuel filters can be a source of air leakage, so remove them for the inital setting. Always install a new glow plug. The object here is to be as sure as possible that other systems won't interfere with the carburetor when we're setting it up. By this point, you should have run the engine a little and found that the carb settings are good enough to start turning the engine. Refer now to the pictures of the carburetors, and identify the one that looks like yours. You only need to identify the idle-mixture screw; the high-speed valve is always the longest and most prominent of the adjustment screws. CARB ADJUSTMENS If you can, have a helper hold the transmitter. Tell your assistant to open the throttle fully when you point you finger upward, and to close it fully when you point your finger downward. 1. Start the engine and, using the throttle trim, set the idle speed. Typically 2,500 to 3,500 rpm is correct. Then test to see whether, with the throttle stick fully down, moving the trim to the full-down position will shut off the engine as an emergency cutoff. Adjust it as required. 2. Open the throttle fully. If the engine speeds up momentarily and then dies, open the highspeed needle valve one turn (richer) and restart. Once the engine is running smoothly, slowly turn the high-speed needle valve clockwise (leaner) until the engine runs maximum rpm. If you turn the needle valve too far, the engine will die. Open it half a turn (richer) and restart. Note: always restart at 1/4 throttle or less. It makes starts easier and safer. By now, you should have a feel for the maximum rpm, so run the engine up to the maximum rpm point and turn the high-speed needle counterclockwise (richer) just until you detect a slight slowing of the engine. This will put the setting a little on the rich side. 3. Now set the idle-mixture screw. For safety, stop the engine when you do this. Refer to the pictures, and find the carb style that matches that on your engine. From the picture, you can determine where to make the idle-mixture adjustment and the direction in which to turn the needle for a rich or a lean mixture. For example, on a two-needle carb such as a Webra, you'd turn the needle counterclock-wise to richen the mixture, becasue the fuel is being metered. With an air blend, such as that found on many Enya engines, you'd turn the screw clockwise to richen the mixture because the air is being metered. Slowly pull the throttle stick on your transmitter down, and have the throttle trim full up (idle position). If the engine quites right away, richen the idle-mixture a little and restart. Repeat this if necessary. If the engine slows down after a little while, runs roughly, and then quits, make the idle mixture leaner. When the engine idles at a reasonably slow speed (3,000 rpm or so), you can fine tune the idle mixture: idle the engine for 30 seconds, then quickly open the throttle fully. If it bogs down, and/or eventually quits, the mixture is too rich; if the engine quits abruptly, it's too lean. Make the suitable adjustments. One it has been set, the idle mixture rarely, if ever, has to be adjusted. 4. Now you can make the final adjustment on the high-speed needle valve. Hold the plane level, open the throttle fully and adjust it as you did before for just-below-maximum rpm. Now point the plane's nose straight up. If the engine stalls, open the needle valve slightly (richer) and try again. Sometimes it's best to make the maximum rpm setting with the nose already up. The engine must run at maximum rpm with the nose up if you want to prevent your engine from stalling just after takeoff. 5. This is very important! Don't change the adjustments you've just made. Don't close the needle valves at the end of a flying session. Leave the settings where they are. The next time you go to the field, just fill up the tank, open the high-speed needle valve (richer) half a turn and start up the engine. When the engine is warm, open the throttle fully and point the plane's nose up. Repeat the final adjustment described in the previous paragraph. TROUBLESHOOTING The only types of needle valves that I've ever had trouble with are those that don't have a spring riding on the straight knurl of the needle body. These are often seen on old K&Bs and old Super Tigres. It's difficult to set their friction locknuts to allow the needles to turn and yet not vibrate loose when the engine runs. I once locked an engine tight on the rich side and flew it all summer without changing it because of just that problem! If you start to notice problems, look elsewhere before you start twisting the needle valves (e.g., check glow plugs, tubing, dirt in fuel system). That's all there is to it! Make your settings; don't change them, and keep 'em flying! TECH TERMS CCW - counterclockwise CW - clockwise High-speed needle valve - sets the flow of fuel to the engine at high speeds (also called the "high-speed mixture valve"). It's always located on the side of the engine opposite the muffler. It's the most prominent needle valve. Idle-speed stop screw - limits the motion of the throttle barrel toward the closed position. It's also called the "idle stop screw," the "throttle stop screw," and the "rotor setscrew." Idle-mixture screw - sets the flow of fuel to the engine at low speeds. It's also called the "air-bleed screw," the "mixture control screw," (on some O.S. engines) and the "low-speed mixture setting screw." It's usually opposite the high-speed needle valve.

Carburetor Basics by BOB GILBERTas appeared in Model Airplane News

<hr size="5" color="#0000ff" />

SET-UP AND OPERATION I'm an old-timer in the hobby, and my motto is "Keep 'em flying." Toward that end, I'll try to help you keep those engines purring! As simple as possible, this guide will enable you to properly set up 90 percent of the carburetors available today. I'll address 2-stroke sport-type engines up to .65 displacement that don't have tuned pipes, pumps, or three-needle valve carbs. THROTTLE? CHECK! FUEL? CHECK! ... To start, set the throttle linkage. If your throttle servo doesn't have an adjustable arm, get one. It will help you immensely when you make these adjustments. (This won't be necessary with newer radios that have servo-travel adjustment built in.) With the linkage disconnected, hold the throttle arm so that you can rotate the barrel toward the closed position. Rotate the idle-speed stop screw so that the barrel closes fully, then rotate it half a turn more. Don't back the screw out any farther, because on some engines this screw also holds the throttle barrel in place. If there's a locknut on the screw, tighten it. Now connect the throttle linkage to the servo, and adjust it so that the with the stick and trim fully down (emergency cutoff position) the barrel is completely closed, and with the stick and trim fully up (full throttle) the barrel will be 100 percent open. For idle, set the trim at the position that will open the throttle barrel 1/32 of an inch (about the size of a round toothpick at its thickest point) when the stick is fully down and the trim is fully up (idle position). Next, check the fuel system. The spraybar/needle-valve assembly should be positioned (relative to the tank) no less than a third, but no more than halfway, down from the top of the tank. The fuel tank will be pressurized with muffler pressure. Inspect all fuel lines, metal and otherwise, for kinks and splits. Look inside the tank unless it's brand new. Fuel filters can be a source of air leakage, so remove them for the inital setting. Always install a new glow plug. The object here is to be as sure as possible that other systems won't interfere with the carburetor when we're setting it up. By this point, you should have run the engine a little and found that the carb settings are good enough to start turning the engine. Refer now to the pictures of the carburetors, and identify the one that looks like yours. You only need to identify the idle-mixture screw; the high-speed valve is always the longest and most prominent of the adjustment screws. CARB ADJUSTMENS If you can, have a helper hold the transmitter. Tell your assistant to open the throttle fully when you point you finger upward, and to close it fully when you point your finger downward. 1. Start the engine and, using the throttle trim, set the idle speed. Typically 2,500 to 3,500 rpm is correct. Then test to see whether, with the throttle stick fully down, moving the trim to the full-down position will shut off the engine as an emergency cutoff. Adjust it as required. 2. Open the throttle fully. If the engine speeds up momentarily and then dies, open the highspeed needle valve one turn (richer) and restart. Once the engine is running smoothly, slowly turn the high-speed needle valve clockwise (leaner) until the engine runs maximum rpm. If you turn the needle valve too far, the engine will die. Open it half a turn (richer) and restart. Note: always restart at 1/4 throttle or less. It makes starts easier and safer. By now, you should have a feel for the maximum rpm, so run the engine up to the maximum rpm point and turn the high-speed needle counterclockwise (richer) just until you detect a slight slowing of the engine. This will put the setting a little on the rich side. 3. Now set the idle-mixture screw. For safety, stop the engine when you do this. Refer to the pictures, and find the carb style that matches that on your engine. From the picture, you can determine where to make the idle-mixture adjustment and the direction in which to turn the needle for a rich or a lean mixture. For example, on a two-needle carb such as a Webra, you'd turn the needle counterclock-wise to richen the mixture, becasue the fuel is being metered. With an air blend, such as that found on many Enya engines, you'd turn the screw clockwise to richen the mixture because the air is being metered. Slowly pull the throttle stick on your transmitter down, and have the throttle trim full up (idle position). If the engine quites right away, richen the idle-mixture a little and restart. Repeat this if necessary. If the engine slows down after a little while, runs roughly, and then quits, make the idle mixture leaner. When the engine idles at a reasonably slow speed (3,000 rpm or so), you can fine tune the idle mixture: idle the engine for 30 seconds, then quickly open the throttle fully. If it bogs down, and/or eventually quits, the mixture is too rich; if the engine quits abruptly, it's too lean. Make the suitable adjustments. One it has been set, the idle mixture rarely, if ever, has to be adjusted. 4. Now you can make the final adjustment on the high-speed needle valve. Hold the plane level, open the throttle fully and adjust it as you did before for just-below-maximum rpm. Now point the plane's nose straight up. If the engine stalls, open the needle valve slightly (richer) and try again. Sometimes it's best to make the maximum rpm setting with the nose already up. The engine must run at maximum rpm with the nose up if you want to prevent your engine from stalling just after takeoff. 5. This is very important! Don't change the adjustments you've just made. Don't close the needle valves at the end of a flying session. Leave the settings where they are. The next time you go to the field, just fill up the tank, open the high-speed needle valve (richer) half a turn and start up the engine. When the engine is warm, open the throttle fully and point the plane's nose up. Repeat the final adjustment described in the previous paragraph. TROUBLESHOOTING The only types of needle valves that I've ever had trouble with are those that don't have a spring riding on the straight knurl of the needle body. These are often seen on old K&Bs and old Super Tigres. It's difficult to set their friction locknuts to allow the needles to turn and yet not vibrate loose when the engine runs. I once locked an engine tight on the rich side and flew it all summer without changing it because of just that problem! If you start to notice problems, look elsewhere before you start twisting the needle valves (e.g., check glow plugs, tubing, dirt in fuel system). That's all there is to it! Make your settings; don't change them, and keep 'em flying! TECH TERMS CCW - counterclockwise CW - clockwise High-speed needle valve - sets the flow of fuel to the engine at high speeds (also called the "high-speed mixture valve"). It's always located on the side of the engine opposite the muffler. It's the most prominent needle valve. Idle-speed stop screw - limits the motion of the throttle barrel toward the closed position. It's also called the "idle stop screw," the "throttle stop screw," and the "rotor setscrew." Idle-mixture screw - sets the flow of fuel to the engine at low speeds. It's also called the "air-bleed screw," the "mixture control screw," (on some O.S. engines) and the "low-speed mixture setting screw." It's usually opposite the high-speed needle valve.

Carburetor Basics by BOB GILBERT as appeared in Model Airplane News

<hr size="5" color="#0000ff" />

SET-UP AND OPERATION I'm an old-timer in the hobby, and my motto is "Keep 'em flying." Toward that end, I'll try to help you keep those engines purring! As simple as possible, this guide will enable you to properly set up 90 percent of the carburetors available today. I'll address 2-stroke sport-type engines up to .65 displacement that don't have tuned pipes, pumps, or three-needle valve carbs. THROTTLE? CHECK! FUEL? CHECK! ... To start, set the throttle linkage. If your throttle servo doesn't have an adjustable arm, get one. It will help you immensely when you make these adjustments. (This won't be necessary with newer radios that have servo-travel adjustment built in.) With the linkage disconnected, hold the throttle arm so that you can rotate the barrel toward the closed position. Rotate the idle-speed stop screw so that the barrel closes fully, then rotate it half a turn more. Don't back the screw out any farther, because on some engines this screw also holds the throttle barrel in place. If there's a locknut on the screw, tighten it. Now connect the throttle linkage to the servo, and adjust it so that the with the stick and trim fully down (emergency cutoff position) the barrel is completely closed, and with the stick and trim fully up (full throttle) the barrel will be 100 percent open. For idle, set the trim at the position that will open the throttle barrel 1/32 of an inch (about the size of a round toothpick at its thickest point) when the stick is fully down and the trim is fully up (idle position). Next, check the fuel system. The spraybar/needle-valve assembly should be positioned (relative to the tank) no less than a third, but no more than halfway, down from the top of the tank. The fuel tank will be pressurized with muffler pressure. Inspect all fuel lines, metal and otherwise, for kinks and splits. Look inside the tank unless it's brand new. Fuel filters can be a source of air leakage, so remove them for the inital setting. Always install a new glow plug. The object here is to be as sure as possible that other systems won't interfere with the carburetor when we're setting it up. By this point, you should have run the engine a little and found that the carb settings are good enough to start turning the engine. Refer now to the pictures of the carburetors, and identify the one that looks like yours. You only need to identify the idle-mixture screw; the high-speed valve is always the longest and most prominent of the adjustment screws. CARB ADJUSTMENS If you can, have a helper hold the transmitter. Tell your assistant to open the throttle fully when you point you finger upward, and to close it fully when you point your finger downward. 1. Start the engine and, using the throttle trim, set the idle speed. Typically 2,500 to 3,500 rpm is correct. Then test to see whether, with the throttle stick fully down, moving the trim to the full-down position will shut off the engine as an emergency cutoff. Adjust it as required. 2. Open the throttle fully. If the engine speeds up momentarily and then dies, open the highspeed needle valve one turn (richer) and restart. Once the engine is running smoothly, slowly turn the high-speed needle valve clockwise (leaner) until the engine runs maximum rpm. If you turn the needle valve too far, the engine will die. Open it half a turn (richer) and restart. Note: always restart at 1/4 throttle or less. It makes starts easier and safer. By now, you should have a feel for the maximum rpm, so run the engine up to the maximum rpm point and turn the high-speed needle counterclockwise (richer) just until you detect a slight slowing of the engine. This will put the setting a little on the rich side. 3. Now set the idle-mixture screw. For safety, stop the engine when you do this. Refer to the pictures, and find the carb style that matches that on your engine. From the picture, you can determine where to make the idle-mixture adjustment and the direction in which to turn the needle for a rich or a lean mixture. For example, on a two-needle carb such as a Webra, you'd turn the needle counterclock-wise to richen the mixture, becasue the fuel is being metered. With an air blend, such as that found on many Enya engines, you'd turn the screw clockwise to richen the mixture because the air is being metered. Slowly pull the throttle stick on your transmitter down, and have the throttle trim full up (idle position). If the engine quites right away, richen the idle-mixture a little and restart. Repeat this if necessary. If the engine slows down after a little while, runs roughly, and then quits, make the idle mixture leaner. When the engine idles at a reasonably slow speed (3,000 rpm or so), you can fine tune the idle mixture: idle the engine for 30 seconds, then quickly open the throttle fully. If it bogs down, and/or eventually quits, the mixture is too rich; if the engine quits abruptly, it's too lean. Make the suitable adjustments. One it has been set, the idle mixture rarely, if ever, has to be adjusted. 4. Now you can make the final adjustment on the high-speed needle valve. Hold the plane level, open the throttle fully and adjust it as you did before for just-below-maximum rpm. Now point the plane's nose straight up. If the engine stalls, open the needle valve slightly (richer) and try again. Sometimes it's best to make the maximum rpm setting with the nose already up. The engine must run at maximum rpm with the nose up if you want to prevent your engine from stalling just after takeoff. 5. This is very important! Don't change the adjustments you've just made. Don't close the needle valves at the end of a flying session. Leave the settings where they are. The next time you go to the field, just fill up the tank, open the high-speed needle valve (richer) half a turn and start up the engine. When the engine is warm, open the throttle fully and point the plane's nose up. Repeat the final adjustment described in the previous paragraph. TROUBLESHOOTING The only types of needle valves that I've ever had trouble with are those that don't have a spring riding on the straight knurl of the needle body. These are often seen on old K&Bs and old Super Tigres. It's difficult to set their friction locknuts to allow the needles to turn and yet not vibrate loose when the engine runs. I once locked an engine tight on the rich side and flew it all summer without changing it because of just that problem! If you start to notice problems, look elsewhere before you start twisting the needle valves (e.g., check glow plugs, tubing, dirt in fuel system). That's all there is to it! Make your settings; don't change them, and keep 'em flying! TECH TERMS CCW - counterclockwise CW - clockwise High-speed needle valve - sets the flow of fuel to the engine at high speeds (also called the "high-speed mixture valve"). It's always located on the side of the engine opposite the muffler. It's the most prominent needle valve. Idle-speed stop screw - limits the motion of the throttle barrel toward the closed position. It's also called the "idle stop screw," the "throttle stop screw," and the "rotor setscrew." Idle-mixture screw - sets the flow of fuel to the engine at low speeds. It's also called the "air-bleed screw," the "mixture control screw," (on some O.S. engines) and the "low-speed mixture setting screw." It's usually opposite the high-speed needle valve.

Carburetor Basics by BOB GILBERT as appeared in Model Airplane News

<hr size="5" color="#0000ff" />

SET-UP AND OPERATION I'm an old-timer in the hobby, and my motto is "Keep 'em flying." Toward that end, I'll try to help you keep those engines purring! As simple as possible, this guide will enable you to properly set up 90 percent of the carburetors available today. I'll address 2-stroke sport-type engines up to .65 displacement that don't have tuned pipes, pumps, or three-needle valve carbs. THROTTLE? CHECK! FUEL? CHECK! ... To start, set the throttle linkage. If your throttle servo doesn't have an adjustable arm, get one. It will help you immensely when you make these adjustments. (This won't be necessary with newer radios that have servo-travel adjustment built in.) With the linkage disconnected, hold the throttle arm so that you can rotate the barrel toward the closed position. Rotate the idle-speed stop screw so that the barrel closes fully, then rotate it half a turn more. Don't back the screw out any farther, because on some engines this screw also holds the throttle barrel in place. If there's a locknut on the screw, tighten it. Now connect the throttle linkage to the servo, and adjust it so that the with the stick and trim fully down (emergency cutoff position) the barrel is completely closed, and with the stick and trim fully up (full throttle) the barrel will be 100 percent open. For idle, set the trim at the position that will open the throttle barrel 1/32 of an inch (about the size of a round toothpick at its thickest point) when the stick is fully down and the trim is fully up (idle position). Next, check the fuel system. The spraybar/needle-valve assembly should be positioned (relative to the tank) no less than a third, but no more than halfway, down from the top of the tank. The fuel tank will be pressurized with muffler pressure. Inspect all fuel lines, metal and otherwise, for kinks and splits. Look inside the tank unless it's brand new. Fuel filters can be a source of air leakage, so remove them for the inital setting. Always install a new glow plug. The object here is to be as sure as possible that other systems won't interfere with the carburetor when we're setting it up. By this point, you should have run the engine a little and found that the carb settings are good enough to start turning the engine. Refer now to the pictures of the carburetors, and identify the one that looks like yours. You only need to identify the idle-mixture screw; the high-speed valve is always the longest and most prominent of the adjustment screws. CARB ADJUSTMENS If you can, have a helper hold the transmitter. Tell your assistant to open the throttle fully when you point you finger upward, and to close it fully when you point your finger downward. 1. Start the engine and, using the throttle trim, set the idle speed. Typically 2,500 to 3,500 rpm is correct. Then test to see whether, with the throttle stick fully down, moving the trim to the full-down position will shut off the engine as an emergency cutoff. Adjust it as required. 2. Open the throttle fully. If the engine speeds up momentarily and then dies, open the highspeed needle valve one turn (richer) and restart. Once the engine is running smoothly, slowly turn the high-speed needle valve clockwise (leaner) until the engine runs maximum rpm. If you turn the needle valve too far, the engine will die. Open it half a turn (richer) and restart. Note: always restart at 1/4 throttle or less. It makes starts easier and safer. By now, you should have a feel for the maximum rpm, so run the engine up to the maximum rpm point and turn the high-speed needle counterclockwise (richer) just until you detect a slight slowing of the engine. This will put the setting a little on the rich side. 3. Now set the idle-mixture screw. For safety, stop the engine when you do this. Refer to the pictures, and find the carb style that matches that on your engine. From the picture, you can determine where to make the idle-mixture adjustment and the direction in which to turn the needle for a rich or a lean mixture. For example, on a two-needle carb such as a Webra, you'd turn the needle counterclock-wise to richen the mixture, becasue the fuel is being metered. With an air blend, such as that found on many Enya engines, you'd turn the screw clockwise to richen the mixture because the air is being metered. Slowly pull the throttle stick on your transmitter down, and have the throttle trim full up (idle position). If the engine quites right away, richen the idle-mixture a little and restart. Repeat this if necessary. If the engine slows down after a little while, runs roughly, and then quits, make the idle mixture leaner. When the engine idles at a reasonably slow speed (3,000 rpm or so), you can fine tune the idle mixture: idle the engine for 30 seconds, then quickly open the throttle fully. If it bogs down, and/or eventually quits, the mixture is too rich; if the engine quits abruptly, it's too lean. Make the suitable adjustments. One it has been set, the idle mixture rarely, if ever, has to be adjusted. 4. Now you can make the final adjustment on the high-speed needle valve. Hold the plane level, open the throttle fully and adjust it as you did before for just-below-maximum rpm. Now point the plane's nose straight up. If the engine stalls, open the needle valve slightly (richer) and try again. Sometimes it's best to make the maximum rpm setting with the nose already up. The engine must run at maximum rpm with the nose up if you want to prevent your engine from stalling just after takeoff. 5. This is very important! Don't change the adjustments you've just made. Don't close the needle valves at the end of a flying session. Leave the settings where they are. The next time you go to the field, just fill up the tank, open the high-speed needle valve (richer) half a turn and start up the engine. When the engine is warm, open the throttle fully and point the plane's nose up. Repeat the final adjustment described in the previous paragraph. TROUBLESHOOTING The only types of needle valves that I've ever had trouble with are those that don't have a spring riding on the straight knurl of the needle body. These are often seen on old K&Bs and old Super Tigres. It's difficult to set their friction locknuts to allow the needles to turn and yet not vibrate loose when the engine runs. I once locked an engine tight on the rich side and flew it all summer without changing it because of just that problem! If you start to notice problems, look elsewhere before you start twisting the needle valves (e.g., check glow plugs, tubing, dirt in fuel system). That's all there is to it! Make your settings; don't change them, and keep 'em flying! TECH TERMS CCW - counterclockwise CW - clockwise High-speed needle valve - sets the flow of fuel to the engine at high speeds (also called the "high-speed mixture valve"). It's always located on the side of the engine opposite the muffler. It's the most prominent needle valve. Idle-speed stop screw - limits the motion of the throttle barrel toward the closed position. It's also called the "idle stop screw," the "throttle stop screw," and the "rotor setscrew." Idle-mixture screw - sets the flow of fuel to the engine at low speeds. It's also called the "air-bleed screw," the "mixture control screw," (on some O.S. engines) and the "low-speed mixture setting screw." It's usually opposite the high-speed needle valve.

<hr size="5" color="#0000ff" />

Carburetor Basics by BOB GILBERT as appeared in Model Airplane News

<hr size="5" color="#0000ff" />

SET-UP AND OPERATION I'm an old-timer in the hobby, and my motto is "Keep 'em flying." Toward that end, I'll try to help you keep those engines purring! As simple as possible, this guide will enable you to properly set up 90 percent of the carburetors available today. I'll address 2-stroke sport-type engines up to .65 displacement that don't have tuned pipes, pumps, or three-needle valve carbs. THROTTLE? CHECK! FUEL? CHECK! ... To start, set the throttle linkage. If your throttle servo doesn't have an adjustable arm, get one. It will help you immensely when you make these adjustments. (This won't be necessary with newer radios that have servo-travel adjustment built in.) With the linkage disconnected, hold the throttle arm so that you can rotate the barrel toward the closed position. Rotate the idle-speed stop screw so that the barrel closes fully, then rotate it half a turn more. Don't back the screw out any farther, because on some engines this screw also holds the throttle barrel in place. If there's a locknut on the screw, tighten it. Now connect the throttle linkage to the servo, and adjust it so that the with the stick and trim fully down (emergency cutoff position) the barrel is completely closed, and with the stick and trim fully up (full throttle) the barrel will be 100 percent open. For idle, set the trim at the position that will open the throttle barrel 1/32 of an inch (about the size of a round toothpick at its thickest point) when the stick is fully down and the trim is fully up (idle position). Next, check the fuel system. The spraybar/needle-valve assembly should be positioned (relative to the tank) no less than a third, but no more than halfway, down from the top of the tank. The fuel tank will be pressurized with muffler pressure. Inspect all fuel lines, metal and otherwise, for kinks and splits. Look inside the tank unless it's brand new. Fuel filters can be a source of air leakage, so remove them for the inital setting. Always install a new glow plug. The object here is to be as sure as possible that other systems won't interfere with the carburetor when we're setting it up. By this point, you should have run the engine a little and found that the carb settings are good enough to start turning the engine. Refer now to the pictures of the carburetors, and identify the one that looks like yours. You only need to identify the idle-mixture screw; the high-speed valve is always the longest and most prominent of the adjustment screws. CARB ADJUSTMENS If you can, have a helper hold the transmitter. Tell your assistant to open the throttle fully when you point you finger upward, and to close it fully when you point your finger downward. 1. Start the engine and, using the throttle trim, set the idle speed. Typically 2,500 to 3,500 rpm is correct. Then test to see whether, with the throttle stick fully down, moving the trim to the full-down position will shut off the engine as an emergency cutoff. Adjust it as required. 2. Open the throttle fully. If the engine speeds up momentarily and then dies, open the highspeed needle valve one turn (richer) and restart. Once the engine is running smoothly, slowly turn the high-speed needle valve clockwise (leaner) until the engine runs maximum rpm. If you turn the needle valve too far, the engine will die. Open it half a turn (richer) and restart. Note: always restart at 1/4 throttle or less. It makes starts easier and safer. By now, you should have a feel for the maximum rpm, so run the engine up to the maximum rpm point and turn the high-speed needle counterclockwise (richer) just until you detect a slight slowing of the engine. This will put the setting a little on the rich side. 3. Now set the idle-mixture screw. For safety, stop the engine when you do this. Refer to the pictures, and find the carb style that matches that on your engine. From the picture, you can determine where to make the idle-mixture adjustment and the direction in which to turn the needle for a rich or a lean mixture. For example, on a two-needle carb such as a Webra, you'd turn the needle counterclock-wise to richen the mixture, becasue the fuel is being metered. With an air blend, such as that found on many Enya engines, you'd turn the screw clockwise to richen the mixture because the air is being metered. Slowly pull the throttle stick on your transmitter down, and have the throttle trim full up (idle position). If the engine quites right away, richen the idle-mixture a little and restart. Repeat this if necessary. If the engine slows down after a little while, runs roughly, and then quits, make the idle mixture leaner. When the engine idles at a reasonably slow speed (3,000 rpm or so), you can fine tune the idle mixture: idle the engine for 30 seconds, then quickly open the throttle fully. If it bogs down, and/or eventually quits, the mixture is too rich; if the engine quits abruptly, it's too lean. Make the suitable adjustments. One it has been set, the idle mixture rarely, if ever, has to be adjusted. 4. Now you can make the final adjustment on the high-speed needle valve. Hold the plane level, open the throttle fully and adjust it as you did before for just-below-maximum rpm. Now point the plane's nose straight up. If the engine stalls, open the needle valve slightly (richer) and try again. Sometimes it's best to make the maximum rpm setting with the nose already up. The engine must run at maximum rpm with the nose up if you want to prevent your engine from stalling just after takeoff. 5. This is very important! Don't change the adjustments you've just made. Don't close the needle valves at the end of a flying session. Leave the settings where they are. The next time you go to the field, just fill up the tank, open the high-speed needle valve (richer) half a turn and start up the engine. When the engine is warm, open the throttle fully and point the plane's nose up. Repeat the final adjustment described in the previous paragraph. TROUBLESHOOTING The only types of needle valves that I've ever had trouble with are those that don't have a spring riding on the straight knurl of the needle body. These are often seen on old K&Bs and old Super Tigres. It's difficult to set their friction locknuts to allow the needles to turn and yet not vibrate loose when the engine runs. I once locked an engine tight on the rich side and flew it all summer without changing it because of just that problem! If you start to notice problems, look elsewhere before you start twisting the needle valves (e.g., check glow plugs, tubing, dirt in fuel system). That's all there is to it! Make your settings; don't change them, and keep 'em flying! TECH TERMS CCW - counterclockwise CW - clockwise High-speed needle valve - sets the flow of fuel to the engine at high speeds (also called the "high-speed mixture valve"). It's always located on the side of the engine opposite the muffler. It's the most prominent needle valve. Idle-speed stop screw - limits the motion of the throttle barrel toward the closed position. It's also called the "idle stop screw," the "throttle stop screw," and the "rotor setscrew." Idle-mixture screw - sets the flow of fuel to the engine at low speeds. It's also called the "air-bleed screw," the "mixture control screw," (on some O.S. engines) and the "low-speed mixture setting screw." It's usually opposite the high-speed needle valve.

OzMo

My Feedback: (3)

sorry it copied funny[:@]

Gray Beard

My Feedback: (-1)

Oz, it's a pretty good thing for new people to have, maybe you should repost it so you don't have to copy it 6 times. That is strange how it did that????

Flyin Beagle

My Feedback: (1)

OZ, That is great info. I have an old K&B motor with that exact carb and no manuals. I have fiddled with it quite a bit , but have always had problems with it bogging down in flight. None of the guys at the field are familiar with it so it is everyones best guess as to what is wrong.Knowing that they have problems with thte needle turning in flightI can figure out a way tostop it . I nowknow what everything does and can work back from there.


Thanks

Jetdesign

My Feedback: (8)

I believe the method of tuning the low end based on transition is only approximate and that there is an easy, better, more reliable, and less subjective method. If you're interested in finding what it is, you can read about it here.

JohnBuckner

My Feedback: (1)

Great OZMO and this one should be a prime candidate for a sticky here in the beginers forum. Iagree withGray Beardespecially since it not only delves into different operationsof a number ofdifferent principle types such as double needles, bleeders, rotating spray bars types and so on.

Having this to point to with the excellent drawings would so simplify trying to figure out what type of carb someone has and trying to help them.

John

CGRetired

My Feedback: (1)

Oz.. can you delete the image, edit out the repeat images, and then re-post?

I tried to do it at the moderator level, but cannot.

CGr.

Regent

Great info on the carbs, thanks a bunch. I have been adjusting the mixture on model engines for a number of years but I have an OS 60 FP with an air bleed carb that has me temporarly stumped. This is an engine that was installed in a model that I bought used. It doesn't appear to have a lot of time on it and has excellent compression and runs very strong on the top end and with a 12X4 APC will pull a 4 lb. 12 oz. model straight up till it is out of sight. I adjust the HSN about 300 RPM below peak but if I pull the throttle back to 50% it immediately load up and eventually dies. The only way to get it to lean out again is to pinch off the fuel line. While the throttle is at 50% it is blowing fuel out the exhaust and will empty a full tank in just a couple of minutes.

Here is the deal.

[*]The tank with all new plumbing is installed with the tank outlet on the same line with the HSN.[*]Tried two different brands of 15% fuel.[*]Tried 2 new glow plugs with different heat ranges with no change.[*]Disassembled and cleaned the carb with no change.[*]Checked the low speed air bleed hole by sticking a small allen wrench the same size through the hole and it is not clogged.[*]Adjusted the servo throw and throttle stop adjustment for max open and close.[*]Adjusted the LSN so that the air bleed is completely uncovered. Even completely removed the LSN and put it in my pocket, no change.[/list]The next thing that I am going to try is to drill out the air bleed so it is a little bit larger. If that doesn't fix it I guess I will have to spring for a carb with a fuel adjustment on the LSN.

To my thinking, any air leaks around the backplate, carb seat or HSN assembly would cause it to run lean, not rich.

Any clues?

OzMo

My Feedback: (3)

Suspect a cloged air intake or that someone redrilled the spraybar hole???? I would pull the carb completely appart and look for signs of "fiddling". It is alo possible someone torqued the needle to hard and flared the needle valve seat.

planebuilder66

My Feedback: (8)

NOOooo! don't drill the air bleed out. First start with cleaning the carb, this is just a measure to ensure it's in good order. Reinstall and read your manual, there will be a base air setting, this will be the carb opening setting, open the barrel to acheive the proper opening distance, now reset you HSN and fire it up, tune for 300 off peak, (use a tach) and now go to idle, use the pinch test to get it close, if it dies when you pinch, close the airbleed down to enrichen the mix and vice versa. Now here's the point, the transition has to be steady throughout the entire range, it should hold a peak rpm, mid rpm and a idle for at least 3-5 minutes, let's face it, when's the last time you flew around on idle? Most air bleeds are limited in tuning, but they are no different than a regular 2 needle setup, you just have a reverse acting adjustment on the idle circuit, instead of fuel, you fine adjust the air supply. I suspect that your too rich on the idle and too lean on the HSN, try leaning the airbleed out and retuning the HSN, the primary barrel gap has to be set correctly in order to achieve proper tunability. Good luck and keep trying to tweak it so it's reliable but smooth in all throttle positions.

Regent

OK guys’ thanks for your responses. This afternoon I figured out the problem. I had an opportunity to compare the carburetor on my OS 60FP with a carburetor off another OS 60FP engine and noted that the HSN seat (which should extend to the center of the barrel) was broken off. I am more than a little annoyed that the fellow that sold me the engine failed to mention this little fact. Sometimes those good bargains don’t work out to be as good as we expected.