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Vacuum hose routing & ICU after a rebuild
I just rebuilt my 12 after taking the engine out to repaint, welding a rust trap in the frame hanger & general cleaning up of the carbs. I took the carb farm apart to clean all the carbs individually. Reassembly was fine with the mechanical parts & the fuel lines but I am having a nightmare trying to figure out where all the vacuum lines go. In summary

1) The ICU up at the headstock has a short vacuum line with a circlip on the end of it. This points towards the RH side of the bike as you sit on it

2) There are 2 spigots on the LH carbs. One is a brass tube on the rear carb and the other is in between the 2 LH carbs ( I know there is also a plastic vent outlet on both sides that doesn't connect to anything and it's in addition to this).

3) I have a piece of vacuum tube with a white plastic Tee that has a long tube & a short short tube

4) there is one other longish piece of vacuum tube.

5) There is a spigot on the underside of the carb farm base with nothing connected to it.

I figured the 3rd leg of the Tee joins the ICU tube but if I do this the other 2 ends won't stretch to join on to anything. Is the ICU on upside down? i.e. should the tube be pointing to the LH side of the bike? It seems to be mounted correctly from the form of the wiring harness,

Also with the carbs stripped, they have been emptied of fuel. The starter is turning the bike over but is there any procedure you need to follow to get petrol back into the carbs or do you just crank the engine for ages to get the fuel system going again?

Would appreciate some help...
#1 06-25-2010, 01:20 AM,
The bike was running fine at first. Just took it out today and it's pouring fuel out of the LH vent pipe that runs between the carbs? Is this due to a poorly connected vacuum line?
#2 07-02-2010, 07:54 AM,
The vacuum source for the ICU is the ported, not manifold vacuum, fitting on number 4 carb.

If gas is pouring out the carb vent the problem is most likely a stuck float or needle valve on that carb.
Ed (Vic) Belanger - 1954-2015
Founder of

#3 07-02-2010, 09:55 AM,

I have a similar issue to the above so I thought I'd just continue this thread

I'm assembling a 84 GL1200 (Europe Spec without secondary air supply) when mounting the carbs I ended up with a problem identifying where the vacume hoses go. Now since this is a Euro spec there are very few vacume lines but I'm still not abl eto sort it out.

I have two hoses and thre potential connection points.
1) On the Ignition Control Unit
2) On the rear left hand intake (manifold)
3) Under the air distributor box (looks like a vacume valve where there are two lines going out, one to each set og carbs) and one intake, this is the one that is "vacant"

Problem is that two tubes (with four ends) and three possible connection points does creat a problem. Would be greatful if someone could help me identify what goes where.

I see from the reply above that "The vacuum source for the ICU is the ported, not manifold vacuum, fitting on number 4 carb". Can you please explain some more what/where I find the "ported vacume". Also what is the number 4 Carb?

If I identify the above, can I then assume that 1) above is the vacum supply to 3) above?

Tanks for any help

#4 01-13-2011, 09:37 AM,
Here is a link to Randakk's article on vacuum hose routing.
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#5 01-13-2011, 07:56 PM,
Perfect Wingy, I was trying to get a pic of the vacuum hose routing to display but since I'm using Open Office couldn't get it to work. I guess I'll have to load Microsoft Word to make it happen but you saved the day.
Ed (Vic) Belanger - 1954-2015
Founder of

#6 01-14-2011, 12:52 AM,
Thanks ! great picture. I must somehow have managed to miss the connection on carb 4.
#7 01-14-2011, 02:16 AM,
When I was rebuilding my carbs, I knew my memory wasn`t very strong, so I decided to make a pictorial catalog of my progress. I was glad I had done so because sure enough, I didn`t have any idea where everything hooked up. I was able to reattach everything without any problems. Now I break out the camera at the start of every project, and it has saved my butt several times. Just a suggestion, hope it helps.
Wayne Allen
If you treat your 1200 right, and trust her, she can and will save your butt from a lot of bad scenes. Just believe in her! Mine has several times.
#8 01-14-2011, 02:38 PM,
Your welcome Vic.
Yeah ... I keep a digital camera close by to take pictures as I dismantle stuff. It has saved alot of head scratching when reassembly time comes, especially if days or weeks go by in between>
Now I use the new ipod touch, as it has a camera built in. I found an app for $3.00 that allows me to take a picture, add text or freehand sketching to the picture and even include audio to describe what I'm doing.
Works great for guys like me that "know where I put" it but can't find it ! :-\
#9 01-14-2011, 11:29 PM,
What is the name of that app as I would like to put it on my Ipod also.
Ed (Vic) Belanger - 1954-2015
Founder of

#10 01-15-2011, 12:45 AM,
The app is called Mental Note.
You will need an ipod touch (the new one with camera is best ) or an iPad.
Oh, yeah ... it also syncs with itunes so you can transfer your notes to your desktop.
I think they have a lite version as well, but I spent the whole $3.00 for the full version.
You will like it!
#11 01-15-2011, 10:20 AM,
I've got the newest Ipod Touch and I'm anxious to try out that app, thanks.
Ed (Vic) Belanger - 1954-2015
Founder of

#12 01-16-2011, 04:38 AM,

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