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Ok. I am about to lose it. I tried getting an answer to this on other forums. But,100's of views and nobody knows. Going to be syncing my carbs. Bike is a 99 cbr 900. I somewhat know what I'm doing. I am confused by these manuals that i have though. I have a factory service manual from honda 96-99 (not original, its copied) and a haynes manual. Anything I mention here is looking at the carbs from the seated position.
Both manuals show different locations for the sync adjusting screws. The factory manual shows them to the left of carbs 1,2,&3. The haynes shows them to the right of 1,2,&3 (which is how they actually are). That is one problem. I don't know which screws adjust which carb. Not that big of a deal though cause I can always find out by just adjusting them.
Both manuals say the base carb is #3 and that it can't be adjusted. Both say the vacuum take off screws/plugs (to attach hose adapters)are on cylinders 1,2,&4. The vacuum take off screws on my bike are under carbs 1,3,and 4. The fuel tap vacuum hose is connected to cylinder 2 manifold. Carb 2 has no take off screw for an adapter and it has the vacuum hose underneath so wouldn't that be the base/master carb? But, I think the idle adjustment cable is going to carb 3 , so that is one reason to believe that is the base carb. Is it possible that the carbs were replaced with a different set? I included some photos just in case. I bought the bike used. The bike runs fine. I just took them apart this winter to clean them. Once I figure out which carb is which and what screw does what , I can start. Thanks a lot. I'm eternally grateful to whoever can help.




 

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Ok. I am about to lose it. I tried getting an answer to this on other forums. But,100's of views and nobody knows. Going to be syncing my carbs. Bike is a 99 cbr 900. I somewhat know what I'm doing. I am confused by these manuals that i have though. I have a factory service manual from honda 96-99 (not original, its copied) and a haynes manual. Anything I mention here is looking at the carbs from the seated position.
Both manuals show different locations for the sync adjusting screws. The factory manual shows them to the left of carbs 1,2,&3. The haynes shows them to the right of 1,2,&3 (which is how they actually are). That is one problem. I don't know which screws adjust which carb. Not that big of a deal though cause I can always find out by just adjusting them.
Both manuals say the base carb is #3 and that it can't be adjusted. Both say the vacuum take off screws/plugs (to attach hose adapters)are on cylinders 1,2,&4. The vacuum take off screws on my bike are under carbs 1,3,and 4. The fuel tap vacuum hose is connected to cylinder 2 manifold. Carb 2 has no take off screw for an adapter and it has the vacuum hose underneath so wouldn't that be the base/master carb? But, I think the idle adjustment cable is going to carb 3 , so that is one reason to believe that is the base carb. Is it possible that the carbs were replaced with a different set? I included some photos just in case. I bought the bike used. The bike runs fine. I just took them apart this winter to clean them. Once I figure out which carb is which and what screw does what , I can start. Thanks a lot. I'm eternally grateful to whoever can help.





You are reading the cylinders from left to right, 1, 2, 3, 4 (closest to the camchain)? Do you have an SC28 engine perhaps?
It really doesn't matter where the plugs are, all you need is a vacuum connection to all four cylinders at the same point so you can compare them.
The synchronisation screws are on the linkages between each carb. Generally you balance #1 to #2, and #3 to #4, then you adjust between #2 and #3 to balance both pairs to each other.
 

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Discussion Starter #3
Thanks for replying bladeracer. I'm reading the cylinders as if I was at the back of the bike looking at the front from left to right 1,2,3,4. Yes 4 would be closest to the cam chain I don't know what kind of engine it is. I assume it's the original. I bought the bike used. I know the plugs don't matter cause 4 hoses get hooked up to 4 carbs. But, I am trying to figure out which is the master carb. I forgot to mention I have the motion pro sync pro tool (u can see the video on youtube to see what I'm talking about). You have to calibrate it before using it. You do that by hooking it up to the master carb. If you look at the manifold (from the tool) it will have one hose left to hook up for the calibration procedure. That hose can only hook up to the #2 carb where the vacuum hose is on my bike. This would be the #3 carb looking at the bike from the front. Is that where I'm confused?
 

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Thanks for replying bladeracer. I'm reading the cylinders as if I was at the back of the bike looking at the front from left to right 1,2,3,4. Yes 4 would be closest to the cam chain I don't know what kind of engine it is. I assume it's the original. I bought the bike used. I know the plugs don't matter cause 4 hoses get hooked up to 4 carbs. But, I am trying to figure out which is the master carb. I forgot to mention I have the motion pro sync pro tool (u can see the video on youtube to see what I'm talking about). You have to calibrate it before using it. You do that by hooking it up to the master carb. If you look at the manifold (from the tool) it will have one hose left to hook up for the calibration procedure. That hose can only hook up to the #2 carb where the vacuum hose is on my bike. This would be the #3 carb looking at the bike from the front. Is that where I'm confused?

The engine number will be SC28 for the 893cc engine and SC33 for the 918cc.
You can calibrate the gauges on any cylinder.
The "master" is usually the one that is adjusted by the idle screw.
 

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Discussion Starter #5
Its the 918cc. I remember seeing that on the case. The guy in the video says the tool has to be calibrated to the master carb. So you cant use any carb. So if 3 is the master, i would have to take off the vacuum screw on carb 3 and attach the adapter to calibrate the syncpro tool. Then the vacuum hose on carb 2 is left open, so would i just plug that up for the calibration process? Im trying my best not to confuse anybody.U would have to see the video to see how the tool works to understand what im saying
 

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Its the 918cc. I remember seeing that on the case. The guy in the video says the tool has to be calibrated to the master carb. So you cant use any carb. So if 3 is the master, i would have to take off the vacuum screw on carb 3 and attach the adapter to calibrate the syncpro tool. Then the vacuum hose on carb 2 is left open, so would i just plug that up for the calibration process? Im trying my best not to confuse anybody.U would have to see the video to see how the tool works to understand what im saying

I think the only reason for calibrating on the master is because that one can't be adjusted without changing the idle. I can't think of any other reason.
All calibration does is ensure all four gauges are starting from the same base, which can be done on any carb.
Maybe you have SC28 carbs on an SC33 engine?
 

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Discussion Starter #7
yeah like i mentioned before, i was wondering if those carbs have been replaced with different ones. Both manuals i have show the vacuum hose coming from under the third carb. As you can see mine is under the second carb. Im going to take a look at the numbers stamped on the carb assembly and see if they are different from the original ones. Im betting they will be.
 

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yeah like i mentioned before, i was wondering if those carbs have been replaced with different ones. Both manuals i have show the vacuum hose coming from under the third carb. As you can see mine is under the second carb. Im going to take a look at the numbers stamped on the carb assembly and see if they are different from the original ones. Im betting they will be.

The vacuum ports are in the cylinder head though aren't they?
Maybe you have an SC28 head?
 

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Discussion Starter #9
Yes. You can see them in the pictures that I attached. They are right under the rubber sleeves that attach the carbs. You can use a Phillips screwdriver or a 8mm socket. There is one under every carb except #2 which has the hose.
 

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Yes. You can see them in the pictures that I attached. They are right under the rubber sleeves that attach the carbs. You can use a Phillips screwdriver or a 8mm socket. There is one under every carb except #2 which has the hose.

Three should be plugged, the fourth supplies vacuum to operate the fuel tap. If you want to supply fuel from the tank while synchronising the carbs you will need a T fitting to do so.
 

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Three should be plugged, the fourth supplies vacuum to operate the fuel tap. If you want to supply fuel from the tank while synchronising the carbs you will need a T fitting to do so.
yeah the second one with the vacuum hose gets hooked up to the tank fuel valve. I have an auxilary tank to use while syncing. Im still confused on the master carb. Can the master carb have a vacuum plug? Cause if my #3 carb is the master, that has a plug. And a plug means u can hook up the syncing tool to that carb to make adjustments. But, the master is not supposed to be adjustable.
 

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yeah the second one with the vacuum hose gets hooked up to the tank fuel valve. I have an auxilary tank to use while syncing. Im still confused on the master carb. Can the master carb have a vacuum plug? Cause if my #3 carb is the master, that has a plug. And a plug means u can hook up the syncing tool to that carb to make adjustments. But, the master is not supposed to be adjustable.

The master carburetor may not be adjustable, but you still need to measure its vacuum so you can synch the others to it. Regardless of whether the port is plugged or not, you still need to have one of the vacuum gauges connected to it.
 

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ok. I think i got it LOL! If not, ill post back. Ill give the synching a try within the next couple days. So when i turn the screws, if nothing is happening to the tools fluid levels ill know that is the master. Thanks a lot . I really appreciate it.
 

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ok. I think i got it LOL! If not, ill post back. Ill give the synching a try within the next couple days. So when i turn the screws, if nothing is happening to the tools fluid levels ill know that is the master. Thanks a lot . I really appreciate it.

If you have a close look at the idle adjuster that will tell you exactly which is the master carburetor.
 

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Discussion Starter #15 (Edited)
Yeah. I did that last night. I loosened the carb assembly up last night and pulled it off and looked at it. The idle adjuster is definitely going to #3 like both manuals say so I guess the manuals are correct on the master carb. But, they were both still wrong on where the vacuum hose comes from. They say it's coming from carb 3 . On my bike it's coming from #2. I just have to figure out the sync adjusting screws now. This is where there is conflicting text and photos in the manuals. I guess I should go by the Haynes and not the factory service manual since the photo in the Haynes shows how the screws are on my carbs. The factory service manual doesn't even show them in the right place! This is odd since I have come across errors in the haynes manual that i had to highlight for future reference. There is one screw on the right side of carb 1, one in between carbs 2&3 , and one on the right of carb 3. Any idea which screw will sync which carb or do i just do a trial and error? I know sometimes one screw will sync a pair.
 

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Yeah. I did that last night. I loosened the carb assembly up last night and pulled it off and looked at it. The idle adjuster is definitely going to #3 like both manuals say so I guess the manuals are correct on the master carb. I just have to figure out the sync adjusting screws now. This is where there is conflicting text and photos in the manuals. I guess I should go by the Haynes and not the factory service manual since the photo in the Haynes shows how the screws are on my carbs. The factory service manual doesn't even show them in the right place! This is odd since I have come across errors in the haynes manual that i had to highlight for future reference. There is one screw on the right side of carb 1, one in between carbs 2&3 , and one on the right of carb 3. Any idea which screw will sync which carb?

Clearly, the adjuster synchs the pair of carbs on each side of it. Do both pairs first, then synch the pairs to each other using the centre adjuster.
 

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Bladeracer, you are my idol! Thanks a lot. I really appreciate your time. Anything you need, you let me know! By the way, I know which forum I'll be coming to when I need help again. :)
 

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First of all have you connected the vacuum gauges to find out how far out the carbs are ?? i think if each carb is within 5 hg they are ok before you start panicking over how to ajust them see how far out they are.i did my carbs and it was quite an easy job to do.
 

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I usually like to know exactly what i am doing before i attempt a procedure. I have no idea what the readings are going to be like. I assume not bad cause the bike ran good last year. It is part of maintenance that should be done every 8k miles or 12 months according to my manual. I like to take care of my bike. I bought the bike used last year and put about 2500 miles on it , so i don't know what was done to it before. I'm just trying to go over it and do everything that I can to make sure it is in top shape for the season.

First of all have you connected the vacuum gauges to find out how far out the carbs are ?? i think if each carb is within 5 hg they are ok before you start panicking over how to ajust them see how far out they are.i did my carbs and it was quite an easy job to do.
 
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