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Balancing your Carburetors
What does "balancing" mean and why do I need to do it to my bike?
Balancing keeps each carburetor working the same amount to deliver the same amount and mixture of gas and air to each cylinder. We determine how "hard" each cylinder is working by measuring the vacuum at each of the carburetors which is provided by the downward motion of the cylinders on the first of the 4 strokes(the opposite of the compression that takes place in the cylinders on the 2nd stroke). There is a pressure "drop" that occurs as you pass by the butterfly throttle valve (the flat circular piece that pivots about its center when you move the throttle grip). The throttle valve will never close all the way - or else the engine would die without another source of air. What balancing does is to make sure that each throttle valve on each carb is allowing the same pressure drop to occur, therefore "sucking" the same amount of gas up through the jets.
OK -now how do I do this?
Each bike is a little different, so I'll try to be general, but keep it specific enough so that you have a clue as to what I'm talking about.
The first thing you'll need to do is to print this page out (unless you have a service manual that will step you through the process). Before you gather your tools up - you will need a set of VACUUM GAUGES. There are basically two different types - the dial type and the mercury type. Sure, you can get good and bad mercury-type gauges, but unless you're planning on really going into business for yourself, the cheaper mercury-type gauges are probably your best bet. You can order them from a number of sources including Dennis Kirk and J.C. Whitney in Chicago - ask for a motorcycle catalog (312)431-6102. When you order the gauges, tell the supplier what kind of motorcycle you have and ask them if you need any special adapters to use the gauge (if you do - it's usually just an extra few bucks).
Now that you've got your balancing "sticks" let's get down to it
Ride the bike around for just a couple of minutes to warm it up. Next, shut the bike off and put it on its center stand.
Disconnect the vacuum line (the small hose) to your fuel tap.
Take the gas tank off. If you can leave the gas line connected and still take the tank off, do so, if not - you'll have to find another container to feed the gas to the carbs. I've heard of people using inverted plastic bottles (thouroughly washed out) with some sort of tapered top to them. Connect the fuel line to the tapered tip, fill the container, invert it, and then poke a small hole in the bottom (which is now up in the air) to allow air to get in, and stick it somewhere above the carbs.
Now there should be one small rubber vacuum tube connected to one of the "nipples" that are either in between the carbs and the engine or they may be on the side of the carbs facing the engine. Pull that end of the small vacuum hose off (the other end was connected to the fuel tap-and you just took that off). You now will need to remove the other vacuum "caps" on each of the carb "nipples" that are in the same place as the hose connection for the fuel tap vacuum line (on the other carbs).The vacuum port caps are usually rubber and either pull off by hand, or with a pair of needle-nose pliers (there may be a clip that holds them in place).
Alright - now you have 4 little tubes or small pipes sticking out from or near the carbs. Next, connect the vacuum gauge lines to each of your carb vacuum nipples. Make sure the tubes are attached tightly, and that there won't be any air leaks.
Next - start the bike without revving the engine above 3,000 rpm or so!!! Actually, opening the throttle doesn't create a big vacuum - but if the engine is running fast, slamming the throttle closed will create a momentary high vacuum situation that might suck mercury into the combustion chambers. That is a REALLY BAD THING - mercury vapor is extremely TOXIC and exposure to it in sufficient quantities and for a certain time has shown to cause brain damage. SO...... don't slam the throttle closed when the gauges are hooked up and the engine is running.
Ok, gauges hooked up, engine warm and running......
Set the idle to spec (or thereabouts)
Look at the gauge - the quantity (usually measured in millimeters or inches of mercury) of vacuum is not nearly as important as whether all of the carbs are pulling the SAME vacuum.
So - to balance them, you will be "finely" adjusting the position of the throttling valves in each of the carbs. If you don't have a manual to show you where the adjusting screws (and locknuts, usually) are, open and close the throttle SLOWLY while you are looking at the carb assembly. Specifically, look inbetween each of the carbs for where they are interconnected - there will be some sort of screw or bolt that you can turn to adjust them.
If you have a 2 cylinder bike, you've only got ONE screw/bolt/locknut to deal with - so loosen the locknut and try turning the screw in either direction until you see that the mercury levels are about the same.
If you have a 4 cylinder bike, you will have THREE screws/bolts/locknuts to adjust. Start by adjusting the screw inbetween the #1 and #2 carbs (counting from either side is OK). Turn the screw until the #1 and #2 carbs are reading about the same vacuum. Now move on to the screw inbetween the #3 and #4 carbs. Balance the #3 to the #4 carb. Lastly - turn the screw in the middle to adjust the #1 & #2 carbs to the #3 & #4 carbs.
Now SLOWLY open and close the throttle a few times, each time bringing the bike over about 3,000 rmps.
Recheck the balancing, and repeat the procedure until each carb is within about a quarter to half inch of the others.
When you're all done, shut the bike off, remove the vacuum gauges, and put everything that you took off, back on. If your carbs were out of balance you will
notice the difference in power and / or gas milage.
Balancing your Carburetors
What does "balancing" mean and why do I need to do it to my bike?
Balancing keeps each carburetor working the same amount to deliver the same amount and mixture of gas and air to each cylinder. We determine how "hard" each cylinder is working by measuring the vacuum at each of the carburetors which is provided by the downward motion of the cylinders on the first of the 4 strokes(the opposite of the compression that takes place in the cylinders on the 2nd stroke). There is a pressure "drop" that occurs as you pass by the butterfly throttle valve (the flat circular piece that pivots about its center when you move the throttle grip). The throttle valve will never close all the way - or else the engine would die without another source of air. What balancing does is to make sure that each throttle valve on each carb is allowing the same pressure drop to occur, therefore "sucking" the same amount of gas up through the jets.
OK -now how do I do this?
Each bike is a little different, so I'll try to be general, but keep it specific enough so that you have a clue as to what I'm talking about.
The first thing you'll need to do is to print this page out (unless you have a service manual that will step you through the process). Before you gather your tools up - you will need a set of VACUUM GAUGES. There are basically two different types - the dial type and the mercury type. Sure, you can get good and bad mercury-type gauges, but unless you're planning on really going into business for yourself, the cheaper mercury-type gauges are probably your best bet. You can order them from a number of sources including Dennis Kirk and J.C. Whitney in Chicago - ask for a motorcycle catalog (312)431-6102. When you order the gauges, tell the supplier what kind of motorcycle you have and ask them if you need any special adapters to use the gauge (if you do - it's usually just an extra few bucks).
Now that you've got your balancing "sticks" let's get down to it
Ride the bike around for just a couple of minutes to warm it up. Next, shut the bike off and put it on its center stand.
Disconnect the vacuum line (the small hose) to your fuel tap.
Take the gas tank off. If you can leave the gas line connected and still take the tank off, do so, if not - you'll have to find another container to feed the gas to the carbs. I've heard of people using inverted plastic bottles (thouroughly washed out) with some sort of tapered top to them. Connect the fuel line to the tapered tip, fill the container, invert it, and then poke a small hole in the bottom (which is now up in the air) to allow air to get in, and stick it somewhere above the carbs.
Now there should be one small rubber vacuum tube connected to one of the "nipples" that are either in between the carbs and the engine or they may be on the side of the carbs facing the engine. Pull that end of the small vacuum hose off (the other end was connected to the fuel tap-and you just took that off). You now will need to remove the other vacuum "caps" on each of the carb "nipples" that are in the same place as the hose connection for the fuel tap vacuum line (on the other carbs).The vacuum port caps are usually rubber and either pull off by hand, or with a pair of needle-nose pliers (there may be a clip that holds them in place).
Alright - now you have 4 little tubes or small pipes sticking out from or near the carbs. Next, connect the vacuum gauge lines to each of your carb vacuum nipples. Make sure the tubes are attached tightly, and that there won't be any air leaks.
Next - start the bike without revving the engine above 3,000 rpm or so!!! Actually, opening the throttle doesn't create a big vacuum - but if the engine is running fast, slamming the throttle closed will create a momentary high vacuum situation that might suck mercury into the combustion chambers. That is a REALLY BAD THING - mercury vapor is extremely TOXIC and exposure to it in sufficient quantities and for a certain time has shown to cause brain damage. SO...... don't slam the throttle closed when the gauges are hooked up and the engine is running.
Ok, gauges hooked up, engine warm and running......
Set the idle to spec (or thereabouts)
Look at the gauge - the quantity (usually measured in millimeters or inches of mercury) of vacuum is not nearly as important as whether all of the carbs are pulling the SAME vacuum.
So - to balance them, you will be "finely" adjusting the position of the throttling valves in each of the carbs. If you don't have a manual to show you where the adjusting screws (and locknuts, usually) are, open and close the throttle SLOWLY while you are looking at the carb assembly. Specifically, look inbetween each of the carbs for where they are interconnected - there will be some sort of screw or bolt that you can turn to adjust them.
If you have a 2 cylinder bike, you've only got ONE screw/bolt/locknut to deal with - so loosen the locknut and try turning the screw in either direction until you see that the mercury levels are about the same.
If you have a 4 cylinder bike, you will have THREE screws/bolts/locknuts to adjust. Start by adjusting the screw inbetween the #1 and #2 carbs (counting from either side is OK). Turn the screw until the #1 and #2 carbs are reading about the same vacuum. Now move on to the screw inbetween the #3 and #4 carbs. Balance the #3 to the #4 carb. Lastly - turn the screw in the middle to adjust the #1 & #2 carbs to the #3 & #4 carbs.
Now SLOWLY open and close the throttle a few times, each time bringing the bike over about 3,000 rmps.
Recheck the balancing, and repeat the procedure until each carb is within about a quarter to half inch of the others.
When you're all done, shut the bike off, remove the vacuum gauges, and put everything that you took off, back on. If your carbs were out of balance you will
notice the difference in power and / or gas milage.
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