Vacuum Hose For Fuel Cut Off Valve

Uncle Phil

Uncle Phil

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In The Holler West Of Nashville, Tennessee
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698
96 and later - where does the 'other' end of the vacuum hose that usually runs to the fuel cutoff valve on the right side between the carbs and the fuel tank connect?
I've look at the Service Manual and it appears to be as clear as mud and I prefer not to have to disassemble one of my other ST1100s to find out.
I cannot see a connect with flashlight either.
Your wisdom will be greatly appreciated!
 
cylinder #3, there's a nipple that it attaches to that should be fairly obvious as I recall, once you get clear access to it.
 
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Image stolen from the "other" ST site; the vacuum hoses attach directly to the intake spigots for the cylinder head, not the carbs. Probably need to lift out the rubber mat to see them clearly. Honestly, are you new to ST's UP???
 
I don't see anything in the service manual that shows it, but I seem to recall when I had the carbs off a few years ago its on a little nipple, but I can't recall the details. I think its in the general area where the carb attaches to the head at the carb boot, but I'm having trouble picturing it in my head at the moment.

edit: yeah, like Terry says I seem to remember it being on the head, but when I look at the head drawings in the service manual I don't see it there, that's why I was starting to doubt myself.
 
Found it - outboard side next to the boot under the mat - that was the 'key' - lifting the mat.
And yes you can reconnect without pulling the carbs.
Back to debugging the cruise control ...

BTW Terry - There may come a day when you get old like me and you can hide your own Easter Eggs ... :biggrin:
 
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So, @Uncle Phil, that was really going to the cylinder number 3, right (the rear one, on the right side) ?

The reason why I'm asking this, is I try to find a way to troubleshoot, or confirm, that the fuel cut off valve is defective.

I have seen in another thread, that when the fuel cut off valve is defective, that vacuum hose that you where refering to, that goes from the cut off valve to one particular cylinder, will then (upon valve failure) act as a direct conduit for fuel to that particular cylinder, wich will make this cylinder running too rich and have a "wet" spark plug.

So, if all the other spark plugs looks good, but the #3 is wet black, that could be a good indication.

Chris
 
ChriSTian_64 said:
So, @Uncle Phil, that was really going to the cylinder number 3, right (the rear one, on the right side) ?

The reason why I'm asking this, is I try to find a way to troubleshoot, or confirm, that the fuel cut off valve is defective.

I have seen in another thread, that when the fuel cut off valve is defective, that vacuum hose that you where refering to, that goes from the cut off valve to one particular cylinder, will then (upon valve failure) act as a direct conduit for fuel to that particular cylinder, wich will make this cylinder running too rich and have a "wet" spark plug.

So, if all the other spark plugs looks good, but the #3 is wet black, that could be a good indication.

Chris
Click to expand...
Pull the vacuum hose of of the valve if there is a hint of any fuel the valve is no good. If you have a hand vacuum pump you can check it to see is it hold vacuum. You can also run it for a bit with the hose off to see if it leaks fuel.
 
ChriSTian_64 said:
So, if all the other spark plugs looks good, but the #3 is wet black, that could be a good indication.
Click to expand...
yes, the shutoff valve is the likely cause of that. The vacuum diaphragm inside the valve will develop a hole or a tear, and the fuel can pass through the diaphragm, and through the vacuum hose into cylinder #3. Most of us just remove the valve and plug the vacuum hose, I think it takes a 6mm bolt as I recall, but don't remember for sure.
 
CYYJ said:
Hi Chris:

Have a look at this post....
Click to expand...

Thanks Michael,

Yes, very informative on how to do the by-pass (and it looks really simple to do), and also very interesting to read all the comments after.
One of those comments, #14, by dwalby, confirmed that it is really the cylinder and plug number 3 that get fouled
(Edit : and while I was typing this, @dwalby just confirmed it again, in this post this time). Thanks dwalby. ;-)

So far, I didn't had any loose of power issue.
I believe I am only at the early stage of failure : probably just a crack, a hole or a tear, in the diaphragm, that is causing a strong fuel smell when I shut the engine. Also noticed a few times a very bad smell from the exaust, at start up (probably from the fouled cylinder). I'm now curious to see what my plugs look like.

I will temporarly bypass my cut off valve too, and have a look and the diaphragm and see if I can change it or replace it.
I know I can also just bypass the valve, but if it is possible, I will try to keep it in line with the circuit. If it fails again, I will fix it again.
 
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Uncle Phil said:
Found it - outboard side next to the boot under the mat - that was the 'key' - lifting the mat.
And yes you can reconnect without pulling the carbs.
Back to debugging the cruise control ...

BTW Terry - There may come a day when you get old like me and you can hide your own Easter Eggs ... :biggrin:
Click to expand...
I'm finding myself having to reading up on procedures before I tear into them lately.
When I did the refurb on my 1991, I could not see these vacuum fittings at all until I pulled the carbs and mat. The area was obscured by 29 years of road grime. I cleaned the V area thoroughly, even polished the little fittings (one was not even finger snug). After reassembly, they are perfectly visible between the carb and head...with the help of a flashlight of course.
Yes, they can be replaced with only the air filter housing removed, with the help of duckbilled pliers, which I use on vacuum hoses that don't want to leave home.
It helps if you are skilled in building ship-in-the-bottle models....so does fluency in words/phrases used to describe abnormal sex acts.
 
when I was doing the sync, the two Vacuum hoses on the left side were attached to each other. On the right side one is plugged and one goes to the cut valve, if I remember correctly. So why is one side joined together and the other side not. Bought used so I don't know, so when I did the bypass I just connected the bypass vacuum hose to the front cylinder. Never had an issue. Does it make a difference, who knows I thought whats good for the left is good for the right.
 
Al st1100 said:
when I was doing the sync, the two Vacuum hoses on the left side were attached to each other. On the right side one is plugged and one goes to the cut valve, if I remember correctly. So why is one side joined together and the other side not. Bought used so I don't know, so when I did the bypass I just connected the bypass vacuum hose to the front cylinder. Never had an issue. Does it make a difference, who knows I thought whats good for the left is good for the right.
Click to expand...

Now that you mention it.....
I replaced all the hoses under/around the carbs on my 1991 last Fall. The left side carb vacuum hoses were connected, with a small black plastic plug, ridge in the middle so it couldn't be inserted too far into either hose, and was 'blank'...no air passage. My suspicion was that they were connected in order to be accessible.
 
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