vacuum and ports on carbs on xj700n

I really need to see what the vac hoses look on an 85 XJ700n. A diagram would be really helpful. I know there are vac caps on the engine side of the carb boots. But what about the airbox side of the carbs? There are 4 brass port things sticking out and if I put my finger over them they are sucking in vacuum, changing the idle. My bike idles awesome but doesn't rev past 3k, it bogs. Therefore I cant ride it. Im thinking this vacuum is related to the issue, but this is my first time ever working on a bike (its my first one!)

any help is appreciated

 

Post a photograph of what you are describing.

In the mean time, ... cap them ... until we sort it out.

 

You know, it sounds like the PO put engine-side carb boots on the airbox side of the carbs... although I don't imagine that would throw off the tuning *that* much; to me it sounds like it's still set too rich.

 

surely the engine side wouldn't fit as the venturi ring is larger on the airbox side? need pics really but sounds like they need to be capped for sure.

 

Im 99% positive they are on the right way. And the tubes Im talking about are ON the carbs themselves. You guys are right, I need some pictures. Ill post some soon. thanks guys

 

It is very unusual to have vacuum ports on the air boots. What is not clear in my mind is if you have two sets of them, one set on the carb boots AND one set on the air boots...?

 

He said they're on the carbs mate, I'm wondering if maybe he means the
float bowl breather tubes that some racks have going between one carb body to the other, although I've only ever seen 2 of them & they weren't brass.

If that's the case they should NOT be blocked as I originally suggested as otherwise the carbs won't fill properly. We'll know what they really are when the pics go up I'm sure

 

The 1985 (XJ700N) carbs have brass ports (much larger than the vac nipples on the intake manifolds) on the carb BODIES, positioned horizontally and tilted towards the "rear" at a about a 45-degree angle. These ports come out of a tube boss located on the left side of the mixture screw extension.

You can see this port clearly on Page 3 of the Carb Vivisection article here:

http://www.xj4ever.com/inside%20your%20carbs.pdf

and it can also be spied on the images on pages 4, 5 and 6, too...........

It needs to be blocked off with a rubber cap.


If they are CALIFORNIA carbs (XJ700NC), they will also have a large brass port pointing pretty much straight upwards coming off the #2 carb, in the same general area.....that port connects to the emissions cannister used on Cali model bikes only.

 

Chacal evens the score on the observation game, I read it as 750 not 700 lol

AND should have guessed from the vac-sucking thing that they wouldn't have been bowl breathers... :roll:

Oops

 

The 85 XJ-700N has Mikuni Carbs.

This break-down from the Yamaha Web site doesn't show the Overflow/Breather Hoses.

http://www.yamaha-motor.com/partviewer/ ... _-_1985%29

This photo from an archived Post shoes Mikuni's with the Hoses attached.

I think they are Atmosphere Vents.
They prevent a vacuum in the Fuel Bowls.
Will act as Overflows too prevent Gas from flooding the Crankcase.

(Scroll down)
http://xjbikes.com/Forums/viewtopic/p=30059.html

 

First link didn't work for me.

 

Huh yeah, just took you to a login page right? :?

 

This link took me right to the 885 700N Carb Schematic.

http://www.yamaha-motor.com/partviewer/ ... _-_1985%29

If you get the Home Page:
Use the "Pull-downs"
>Motorcycle
>>Date
>>>Model
>>>>Component

 

Cant find it you must have to be logged in I guess

 

Go to the Parts and Service HOME Page.
Click: View Parts Catalog.
On next screen --> Lower Right.
Click: Proceed to Parts Catalog
On next screen --> Pull-down Menus begin:
>Step 1: Select Motorcycle
>>Step 2: Select 1985
>>>Step 3: Select Maxim - XJ700N - 1985
>>>>Step 4: Select from various options for individual Parts. ( Carbs )

http://www.yamaha-motor.com/sport/servi ... /home.aspx

 

as soon as I click on the parts catalog, it takes me to a login page. Does not go to parts catalog.

Maybe it's where I am, but it won't let me proceed to parts cat... Yamaha doesn't like English people lol.

No matter, as long as the o/p can find it all's good :wink:

 

Apparently, the Parts View I used as a source led me to believe you were equipped with Mikuni's.

I have been advised that your Model is fitted with Hitachi's.

Do Not use the archive photo as a guide.
Those are Mikuni's.
Therefore, the information supplied relating to Mikuni Carbs does not apply to your Bike.

 

Thanks for all the replys guys. But Im still pretty cunfused lol. Here are pictures of the brass ports ucking in vacucum.




now te right side of the carbs.

 

The second and third pics at the airbox side, those 2 are T-pieces joining 2 carbs directly above the fuel rail right? They shouldn't suck vacuum as I understand it and are just float bowl vents so shouldn't be plugged. Do double check though to make sure they aren't pulling vac.

Not sure of the outer ones, maybe emissions related but if they pull vac then plug them & the bike will no doubt thank you with better running

 

Copied from Chacal's post on page 1

The 1985 (XJ700N) carbs have brass ports (much larger than the vac nipples on the intake manifolds) on the carb BODIES, positioned horizontally and tilted towards the "rear" at a about a 45-degree angle. These ports come out of a tube boss located on the left side of the mixture screw extension.

You can see this port clearly on Page 3 of the Carb Vivisection article here:

www.xj4ever.com/inside...0carbs.pdf

and it can also be spied on the images on pages 4, 5 and 6, too...........

It needs to be blocked off with a rubber cap.


^ This sounds like the smaller BRASS ones shown on your pics 1 and 4, and I assume from his wording these will be on all of your carbs although much more hidden on the inside ones. As Len says, these DO need to be blocked.

The larger ones in your pics 2 and 3 that are NOT brass shouldn't be pulling vac, as per my last post they should just be vent tubes but do check

 

Pic 1 + 4 are the "vac ports" that should be blocked off..... (there should be 1 on each carb!)

Pic 2 + 3 are your fuel overflow/breathers

 

Thanks guys! its definitely running better, but now it doesnt want to idle or rev up with out bogging. Ill do some researching on syncing the carbs and see what that does 8O

 

Where are your pilot screws set at? I'd expect if the PO ran it with the leaks he may have wound them way out to try to correct it