Locating vacuum hose connection for fuel petcock?

[claytonia]

I've had a hell of a time getting this bike running like it was prior to fixing the starter and voltage issues. Just not right at all, virtually un-rideable. So by the time winter temps hit last year, I pretty much gave up on it - starts up easily, but one cylinder clearly missing. I just had the feeling I missed something pretty obvious because there's good spark, fuel delivery, and compression in all cylinders. Checked the vacuum hoses, etc. (but...see below). So I bought a new Yamaha Tracer 9 GT (fuel injection! ABS! Traction and skid control!) - which will be my all purpose sport-tourer now. I was just wishing the ST went away - although it's a beautiful, low mileage, comfortable ride - I find myself no longer enjoying working on my bikes (at least with these types pf problems). But then something hit me - in bypassing the petcock, to eliminate fuel delivery as a cause, I don't recall plugging the vacuum tube that operated it. I'm looking at my other post (about the starting issues) and the last message from Ron: "Don't forget to plug the vac. hose"! OK...so my question is, where does this hose connect (to the #3 carb, I think)? I've been looking all around that area and see nothing disconnected. Parts diagrams don't really show it as far as I can see. I'll check the shop manual again. But can someone maybe suggest what I can do about this? I'm pretty embarrassed, as I usually make notes and label everything during disassembly on jobs like this. It runs like it has just such an air/intake leak.

Thanks in advance....

 

[Bush]

Unless you physically removed that vacuum hose when you discarded the fuel valve, it should still be sitting in the area. Look for an unconnected hose. If it isn't there, then you need to put one on the nipple near the #3 cylinder intake and plug the end, or just plug the nipple. Removing the air filter housing will make the job easier.

 

[Ron]

I use one of the bracket screws to plug the vac. line. I leave the hose in place and screw the screw into the vac. valve end of the hose.

 

[claytonia]

Thanks so much for the replies. I have all of the vacuum hoses used for synching the carbs plugged, but I don't see any other one connected to the #3 carb, or the nipple where it is supposed to connect. The synching hoses all attach to the nipples on the intake manifold, but I don't see any other nipple (or hose connected to it) on the #3 carb. But then I don't really know where to look, which is the problem I currently have.

 

[dwalby]

there is no "other" one for the #3 cylinder, there's only one. If you removed the fuel shutoff valve and plugged the #3 vacuum line coming from the nipple, then that's all there is for cylinder #3.

 

[jfheath]

The hose doesn't come from the carb, and at no point does it attach to the carb. it comes from near the air inlet port which is buried in the Vee of the engine. Point your finger on top of the cylinder head cover, right hand side, of the bike, near the rear spark plug. Slide your finger up the cover and over the top. You are now pointing down to the place where the tube attaches.

It is difficult to see because it is dark down there and the rubber insulation sheets get in the way.

Even if just one of those connection points tubes is detached or is not capped, the engine will splutter and pop and have virtually no power. 0 to 50 mph in about 2 minutes.

3 of the four tubes that come up from the bottom of the vee will be plugged. They have a plastic adapter which is there to attach a vacuum gauge in order to balance the carbs. The adapter has a cap over the end which is held in place with a circular spring clip.

Except.....

The one that you are referring to - rear right cylinder, isn't normally plugged. It has a longer tube that attaches to the fuel shut off valve - the 'petcock. The constant pulses of vacuum keep the fuel flowing when the engine is running, and more importantly, shuts it off when the engine isn't running. Without this in place, a tip over could result in fuel flowing onto a hot engine. I have noticed that a few people have by-passed the petcock when the rubber diaphragm in the petcock has failed. If they do this, then the longer tube that attached to the petcock also has to be capped, or the port to which it attached has to be capped.

I use the term 'cap' rather than 'plug' because 'plug' could suggest a permanent blocking of the port. Those 4 ports need to be available for balancing the carbs.

 

[claytonia]

there is no "other" one for the #3 cylinder, there's only one. If you removed the fuel shutoff valve and plugged the #3 vacuum line coming from the nipple, then that's all there is for cylinder #3.

Thanks for the reply.

All 4 carbs have plugged vacuum hoses for synching, attached to their respective manifold nipples. So if there is no other hose, where does the petcock get its vacuum feed from? I've just seen references to the #3 cylinder (which makes sense as it's closest). But I certainly don't see this hose or nipple.

I will try John's suggestion and see if I can find anything.

 

[dwalby]

Thanks for the reply.

All 4 carbs have plugged vacuum hoses for synching, attached to their respective manifold nipples. So if there is no other hose, where does the petcock get its vacuum feed from? I've just seen references to the #3 cylinder (which makes sense as it's closest). But I certainly don't see this hose or nipple.

I will try John's suggestion and see if I can find anything.

The #3 vacuum hose normally was connected to the petcock. In stock form its not plugged. To do a carb sync you disconnect it from the petcock and do one of two things:

1. draw a vacuum on the petcock with a spare hose and clamp it off so the petcock remains flowing
2. put a "T" in the #3 line and attach one hose from the T to the carb sync tool and the other to the petcock to keep the fuel flowing.

Since your petcock is removed, now #3 is plugged just like the other cylinders. There was never a second hose.

 

[Uncle Phil]

Look under the carb mat and there is nipple at the back on the right side IIRC.

 

[dwalby]

Look under the carb mat and there is nipple at the back on the right side IIRC.

If I understand him, he's already found all 4 hoses, but he's looking for a 5th one that doesn't exist.

 

[claytonia]

The hose doesn't come from the carb, and at no point does it attach to the carb. it comes from near the air inlet port which is buried in the Vee of the engine. Point your finger on top of the cylinder head cover, right hand side, of the bike, near the rear spark plug. Slide your finger up the cover and over the top. You are now pointing down to the place where the tube attaches.

It is difficult to see because it is dark down there and the rubber insulation sheets get in the way.

Even if just one of those connection points tubes is detached or is not capped, the engine will splutter and pop and have virtually no power. 0 to 50 mph in about 2 minutes.

3 of the four tubes that come up from the bottom of the vee will be plugged. They have a plastic adapter which is there to attach a vacuum gauge in order to balance the carbs. The adapter has a cap over the end which is held in place with a circular spring clip.

Except.....

The one that you are referring to - rear right cylinder, isn't normally plugged. It has a longer tube that attaches to the fuel shut off valve - the 'petcock. The constant pulses of vacuum keep the fuel flowing when the engine is running, and more importantly, shuts it off when the engine isn't running. Without this in place, a tip over could result in fuel flowing onto a hot engine. I have noticed that a few people have by-passed the petcock when the rubber diaphragm in the petcock has failed. If they do this, then the longer tube that attached to the petcock also has to be capped, or the port to which it attached has to be capped.

I use the term 'cap' rather than 'plug' because 'plug' could suggest a permanent blocking of the port. Those 4 ports need to be available for balancing the carbs.

Thanks for the prompt reply!

Assuming I am looking for a hose the same size as the carb synching hoses (that's the size of the nipple on the petcock), attached is a shot of the only one I see down in the V (attached to the cap in the photo), besides the carb drain hoses and synch hoses. I did a sketch of what (as best as I can tell) is going on here. Is the hose coming off of the T near the cap but not connected to the #2 and #4 carb synch hoses maybe what I'm looking for? It drops down to where I can no longer see it's end, but I can pull on it - if it isn't connected to anything down there.

 

[claytonia]

From the parts diagrams, what I'm looking for is hose #44 in this screen capture. But it doesn't show where it goes, it just ends (not real helpful!)

I really appreciate everyone's responses and advice! I should of course always take photos and/or make sketches before disassembling anything this involved - but I guess I expected to get it back together before I forgot, which clearly didn't happen!

 

[John OoSTerhuis]

Aw geeeze. Your picture is of the hose to the air suction valve (AKA PAIR), fed by a tap/T off/joining #2 and #4 intake manifold hoses. The numbering in your schematic is wrong. Right front is #1, left front is #2, right rear is #3, and left rear is the base carb #4. I’ll look for a picture to try to clear up the confusion.

Always helps to have the Honda Service Manual when you attempt maintenance like this.

John

 

[Uncle Phil]

If I understand him, he's already found all 4 hoses, but he's looking for a 5th one that doesn't exist.

Well, at least one of us understands! I know I went looking for the one I mentioned and couldn't find til someone said it was under the carb mat.

 

[John OoSTerhuis]

Looked at the schematic again. If I’m rereading it correct, what he’s showing is the left side bank with the 2 and 4 carbs feeding the PAIR valves via the hose that T’s to each of them, only one shown. The schematic doesn’t depict the right side, 1 and 3 carbs’ hoses.

Somebody post a picture of the hose arrangements under the carbs of an ST1100 with the PAIRs installed.

 

[Oldbikefixr]

Last time I was into our 1991 I replaced all the water, fuel, air and vacuum tubes and hoses 'cause I didn't want to have to remove the carbs again any time soon to fix leaks on 31 year old hoses. I put a 't' into the vac hose going to the fuel shutoff valve and ran the extra hose up. Made all four extra length, enough that I could clamp them to the frame member on each side of the carbs. The two photos show the right side carbs...the fuel valve is unbolted so I could photo the 't'. Second photo shows the finished location of the lengthened hoses....no more fishing for them next time the carbs need synching.
Just a note, two of the vac hose fittings on the intake manifolds were loose, one extremely loose.

 

[claytonia]

Looked at the schematic again. If I’m rereading it correct, what he’s showing is the left side bank with the 2 and 4 carbs feeding the PAIR valves via the hose that T’s to each of them, only one shown. The schematic doesn’t depict the right side, 1 and 3 carbs’ hoses.

Somebody post a picture of the hose arrangements under the carbs of an ST1100 with the PAIRs installed.

Thanks as always for your input John. I didn't show the right side because, at least on my bike, the #1 and 3 carb synch hoses aren't connected to anything, and are capped as they should be. They aren't involved in the problem I'm having trying to locate a possibly open vacuum hose. So is that the PAIR valve in my photo? That's part of the emissions control, right? Injects air into the intake path or something. But any idea where that hose (off of the T fitting from the PAIR valve) goes in my sketch? The one with the big "?".

"Somebody post a picture of the hose arrangements under the carbs of an ST1100 with the PAIRs installed." - yes, that would be VERY helpful obviously, if someone happens to have a shot of this.

 

[claytonia]

Last time I was into our 1991 I replaced all the water, fuel, air and vacuum tubes and hoses 'cause I didn't want to have to remove the carbs again any time soon to fix leaks on 31 year old hoses. I put a 't' into the vac hose going to the fuel shutoff valve and ran the extra hose up. Made all four extra length, enough that I could clamp them to the frame member on each side of the carbs. The two photos show the right side carbs...the fuel valve is unbolted so I could photo the 't'. Second photo shows the finished location of the lengthened hoses....no more fishing for them next time the carbs need synching.
Just a note, two of the vac hose fittings on the intake manifolds were loose, one extremely loose.

Thanks so much for your input - I really appreciate it. I get what you did, and in fact it wouldn't be a bad idea if I replaced all those vacuum hoses (mine is a 1993). I replaced the carb boots because they were just getting hard and brittle, so like you I then worried about the other rubber items. But my synch hoses all seemed pretty flexible, but I will check the connections to the manifold.

So, as to my problem locating the vacuum feed to the petcock - can you tell me where it originates? That's what I'm trying to determine, because it certainly runs like there's a significant air leak somewhere. And I still haven't ID'd where the hose to the petcock comes from.

 

[dwalby]

So, as to my problem locating the vacuum feed to the petcock - can you tell me where it originates? That's what I'm trying to determine, because it certainly runs like there's a significant air leak somewhere. And I still haven't ID'd where the hose to the petcock comes from.

the question has been answered already, the hose to the petcock comes from the nipple on cylinder #3. If the petcock is removed, that hose gets plugged. There was never a separate hose for carb sync and another hose for the petcock, which I think is your assumption, but that isn't correct.

 

[claytonia]

the question has been answered already, the hose to the petcock comes from the nipple on cylinder #3. If the petcock is removed, that hose gets plugged. There was never a separate hose for carb sync and another hose for the petcock, which I think is your assumption, but that isn't correct.

OK thanks. So you're saying when synching the carbs, you pull the hose off the petcock and use that? That's not how I did it when I last synched my carbs - there are two plugged hoses on the right side and the two connected to the T on the left side.