Balancing carbs
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8,355 Posts
Obviously you need a Carb balancer.I use the superb Carbtune2,
http://www.carbtune.com/
I made an auxiliary fuel tank with a small screw in the bottom that can be removed to allow for the vacuum created and to make it seal a small patch of old inner tube rubber that it screw through that I super-glued in place.
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The pipes need restrictors in them in them(Supplied with the Carbtune2) as the Vacuum created at the carbs is too large to be useful and accurate without them.
Also supplied are the adaptors required to go into the bleed-off points on the carb inlets.
With apparatus setup and with the bike at a maximum of high idle e.g 1100 rpm + 10% max release the 8mm locking nut on the balance adjuster and adjust until the two levels in whatever device you use are level.You don't have to worry about numbers just that they are level.
The Trick:
To allow for the tightening of lock-nut taking the balance out set the balance ever so slightly out and then use the tension of tightening the lock nut to bring them perfectly level.When level and tightened lock the nut in place by degreasing with some carb/brake cleaner and some tissue on a screwdriver and apply some thread-lock.
Note:some people get frustrated when balancing the carbs and hold the throttle at higher revs and seeing the balancer level out and wrongly assume they have balanced their carbs for higher revs.This is incorrect as the vacuum created above 2,000 revs nullifies the balancer making it useless.
This can also lead to premature engine wear/failure as it may cause uneven stress on the crank-shaft over time and possibly uneven heat cycles in the heads a symptom of which may be blowing heads gaskets under long sustained riding.
All carburettor manufactures recommend balancing at the bike/engines idle speed as per above
Source: John(Sean) Morgan manufacturer of the World renowned CarbTune 2.
http://www.carbtune.co.uk/carbcust5.html
http://www.youtube.com/watch?v=xcu3veeQolo
http://www.carbtune.com/
I made an auxiliary fuel tank with a small screw in the bottom that can be removed to allow for the vacuum created and to make it seal a small patch of old inner tube rubber that it screw through that I super-glued in place.
The pipes need restrictors in them in them(Supplied with the Carbtune2) as the Vacuum created at the carbs is too large to be useful and accurate without them.
Also supplied are the adaptors required to go into the bleed-off points on the carb inlets.
With apparatus setup and with the bike at a maximum of high idle e.g 1100 rpm + 10% max release the 8mm locking nut on the balance adjuster and adjust until the two levels in whatever device you use are level.You don't have to worry about numbers just that they are level.
The Trick:
To allow for the tightening of lock-nut taking the balance out set the balance ever so slightly out and then use the tension of tightening the lock nut to bring them perfectly level.When level and tightened lock the nut in place by degreasing with some carb/brake cleaner and some tissue on a screwdriver and apply some thread-lock.
Note:some people get frustrated when balancing the carbs and hold the throttle at higher revs and seeing the balancer level out and wrongly assume they have balanced their carbs for higher revs.This is incorrect as the vacuum created above 2,000 revs nullifies the balancer making it useless.
This can also lead to premature engine wear/failure as it may cause uneven stress on the crank-shaft over time and possibly uneven heat cycles in the heads a symptom of which may be blowing heads gaskets under long sustained riding.
All carburettor manufactures recommend balancing at the bike/engines idle speed as per above
Source: John(Sean) Morgan manufacturer of the World renowned CarbTune 2.
http://www.carbtune.co.uk/carbcust5.html
http://www.youtube.com/watch?v=xcu3veeQolo
Joined
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87 Posts
There is a Philips screw on each intake next to the cylinder head that acts as a vacuum port when the screw is removed. As part of your home-made apparatus, you would need some sort of adapter on the end of your hoses that will screw in to that port. As Shep says, you may also have to experiment with restrictors to get a measurable amount of vacuum.
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2,551 Posts
Padair,
Here are a few pictures to show you where the vacuum tubes go from the balancer that you choose. The tubes that go into the intake manifolds have M5 X 0.8 mm threads. You could buy a long brass bolt and drill the center of it out after cutting the head off it to connect the vacuum lines to.
As for the restrictors Shep is referring to, they usually go into the tip of the vacuum hoses. Mine have a .025 hole in them to cushion the strong vacuum signal. It smooths it out so you'll be able to get an even reading when the engine is running. If they are not restricted the indicator in the tube will bounce up and down and you won't be able to read it accurately.
As stated above when your balancing the carbs it only takes a tiny amount of movement on the center adjustment screw to make a difference in the balance. When you loosen the lock nut, (just enough to let the center screw move), turning the adjuster counter clockwise will raise the vacuum for the right side carb and the indicator will rise higher in the tube. Turning the adjuster screw clockwise will lower the vacuum for the right carb letting the level go lower in the tube.
Don't be tempted to get a balanced level with the nut loose and then tighten it up. Adjust in very small amounts and then tighten up the lock nut. Then snap the throttle a few time so the connecting linkage between the carbs centers itself before you take the reading. It needs to settle again in it's centered position after you have moved it around with the screw driver and 8mm wrench/tool. As Shep mentioned, you can get small amounts of adjustment by tightening the nut a little more. But it won't do much if the balance is way off. And be careful you don't strip the nut tightening it up too much. It's just holding the screws position, not holding the wheel on the bike. Go firm enough to do the job.
Be patient. It takes a while sometimes to get it correct. It can get frustrating when your doing it for the first time.
Here are a few pictures to show you where the vacuum tubes go from the balancer that you choose. The tubes that go into the intake manifolds have M5 X 0.8 mm threads. You could buy a long brass bolt and drill the center of it out after cutting the head off it to connect the vacuum lines to.
As for the restrictors Shep is referring to, they usually go into the tip of the vacuum hoses. Mine have a .025 hole in them to cushion the strong vacuum signal. It smooths it out so you'll be able to get an even reading when the engine is running. If they are not restricted the indicator in the tube will bounce up and down and you won't be able to read it accurately.
As stated above when your balancing the carbs it only takes a tiny amount of movement on the center adjustment screw to make a difference in the balance. When you loosen the lock nut, (just enough to let the center screw move), turning the adjuster counter clockwise will raise the vacuum for the right side carb and the indicator will rise higher in the tube. Turning the adjuster screw clockwise will lower the vacuum for the right carb letting the level go lower in the tube.
Don't be tempted to get a balanced level with the nut loose and then tighten it up. Adjust in very small amounts and then tighten up the lock nut. Then snap the throttle a few time so the connecting linkage between the carbs centers itself before you take the reading. It needs to settle again in it's centered position after you have moved it around with the screw driver and 8mm wrench/tool. As Shep mentioned, you can get small amounts of adjustment by tightening the nut a little more. But it won't do much if the balance is way off. And be careful you don't strip the nut tightening it up too much. It's just holding the screws position, not holding the wheel on the bike. Go firm enough to do the job.
Be patient. It takes a while sometimes to get it correct. It can get frustrating when your doing it for the first time.
Joined
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219 Posts
A quick tip that worked for me - instead of an auxiliary tank, I placed my regular tank back back where the seat normally goes, and used a 2 foot piece of fuel line to go from the petcock to the carb. Bungee cord the tank down and have at the balancing act.
Padair,
Here are a few pictures to show you where the vacuum tubes go from the balancer that you choose. The tubes that go into the intake manifolds have M5 X 0.8 mm threads. You could buy a long brass bolt and drill the center of it out after cutting the head off it to connect the vacuum lines to.
As for the restrictors Shep is referring to, they usually go into the tip of the vacuum hoses. Mine have a .025 hole in them to cushion the strong vacuum signal. It smooths it out so you'll be able to get an even reading when the engine is running. If they are not restricted the indicator in the tube will bounce up and down and you won't be able to read it accurately.
As stated above when your balancing the carbs it only takes a tiny amount of movement on the center adjustment screw to make a difference in the balance. When you loosen the lock nut, (just enough to let the center screw move), turning the adjuster counter clockwise will raise the vacuum for the right side carb and the indicator will rise higher in the tube. Turning the adjuster screw clockwise will lower the vacuum for the right carb letting the level go lower in the tube.
Don't be tempted to get a balanced level with the nut loose and then tighten it up. Adjust in very small amounts and then tighten up the lock nut. Then snap the throttle a few time so the connecting linkage between the carbs centers itself before you take the reading. It needs to settle again in it's centered position after you have moved it around with the screw driver and 8mm wrench/tool. As Shep mentioned, you can get small amounts of adjustment by tightening the nut a little more. But it won't do much if the balance is way off. And be careful you don't strip the nut tightening it up too much. It's just holding the screws position, not holding the wheel on the bike. Go firm enough to do the job.
Be patient. It takes a while sometimes to get it correct. It can get frustrating when your doing it for the first time.
Cool, thanks! The pictures help immensely.
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3,509 Posts
What year is your bike?,if it is an 81 or 82 it probably has a vacuum petcock that would also need to be hooked up. Also if it has a vacuum petcock and you use an auxiliary tank, you need to block off the vacuum port to balance the carbs.
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4,630 Posts
i think what Allan means is......if you have 3 ports to your petcock,you probably have a vacumn port on your carb to make it work.
if so,you will need to block the hole to the carb,a tube and a golf tee work well.
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85 Posts
what tool do you guys use? I have one of these (Motion pro carb sync tool), will it work?
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what tool do you guys use? I have one of these (Motion pro carb sync tool), will it work?
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Those are great. You can get by without, I found you needed to set just a bit off before tightening the nut, which would put it back in sync. It's a bit of trial and error to get the right amount "off"
I made my own balancer last year with some clear tubing, a drywall T, zip ties and a ladder. I used the acid bottle I got with my battery as an aux tank which rested atop the ladder.
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