vacuum hoses, air suction valve? HELP - CBR Forum - Enthusiast forums for Honda CBR Owners


CBR 900RR 1993 - 1999 Honda CBR 900RR

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Old 06-10-2009, 01:43 AM
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Default vacuum hoses, air suction valve? HELP

ok.. i have a 1996 cbr 900

i removed my vacuum hoses, my airbox, carbs, AC canister...

i cant figure out what goes where.. id like to leave out the canister and emissions stuff. i just want to know what the hoses on top of my carbs are for.

it seems like theres one small hose coming from each carb going up. they all collide at a 4 into 1 fitting. then the hose goes around the left side i think, and i dont know what its supposed to fit into. im having trouble with the bike running rough. im going to clean the carbs, but when i put it back together i dont know what to do about these hoses.

im also confused about the three nipples that go into the intake manifold. theres a gold one thats a little deeper than the other two. the gold ones on cyl number three intake, and the other similar two are on one and four. i dont know whats supposed to plug into that, id assume i can plug those.

i also have an aftermarket petcock and theres no vacuum line going to my tank. i dont know if i need one, i thought i just needed it vented to allow flow. right now theres just the nipple coming from the tank with nothing on it.

please help.

what are the 4 hoses atop the carbs?

what are the purposes of the 3 intake tap nipples?

thank you...
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Old 06-10-2009, 01:47 AM
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heres a picture of the intake nipples i cant understand. the gold one in the middle enters the intake stack slightly deeper than the other two
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Old 06-10-2009, 01:52 AM
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this is a picture of carbs similar to mine. the hose i dont know what it does or what its supposed to connect to is the one that runs down the right side..
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Old 06-10-2009, 01:22 PM
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the hose going down the right side is just a overflow tube i think. It is open to air and on my 99 it has a little hook braket that it fits into. im not sure about the other three though. Does it have a gravity fed petcock or a fuel pump. mine has a hose coming from #2 to the petcock. It is the suction hose that opens the diaphragm.
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Old 06-10-2009, 03:44 PM
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its a gravity feed petcock theres no fuel pump.

so i guess i figured it out.. theres a little diagram on the top of the air box. i didnt understand it before but i kept looking at pictures on this forum and i put it together and think i got it right. the bike seems to run smooth but i havent ridden it yet ..(under load)

im about to go for a ride. ill let you know.

thanks
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Old 02-28-2018, 09:15 PM
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Default three nipples

those three nipples should be where you hook up a manometer vacuum gauge to sync the carbs if you have split them apart or if they are out of sync for other reasons, but its rare you need to do it unless you do a major modification and any other time they should just be plugged off. the reason that one of the four is different from the other three and isnt a nipple is because they always sync to one carb from the factory, usually cylinder 2 which it looks like is the one in your pic that isnt a nipple. so cylinder 2 carb is your main butterfly that the rest would be adjusted to by adjusting the set screws on the throttle assembly between each carb to make them open and close in sync. honda says they can be up to a half inch out and that its usually the last thing to do if tuning up your bike full on. it doesnt really change a lot in your bike as far as driving, it will still run even if they are out of sync but you can hear a change and smooth idle with just a better sound over all once they are in sync, you can find some videos on it on youtube with home made manometers which are used by many motorcycle mechanics due to the accuracy of the liquid in home made style as opposed to gauges which bounce around a lot in the store bought ones.
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Old 02-28-2018, 09:41 PM
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Really old thread Stewart. Nice reply, but let's try to keep it current.
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