Locating vacuum hose connection for fuel petcock?

[dwalby]

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.

yes, that's what I've been saying all along in this thread.

here's the service manual page that confirms it



that's the only hose connected to the #3 cylinder, so if the petcock is permanently removed, that's the line that you must plug. It sounds like you've done that, so you've done everything that needs to be done.

Regarding a possible vacuum leak, any chance that one of your 4 plugged vacuum lines has either a split in the hose, or a leak in the plug?

 

[John OoSTerhuis]

So is that the PAIR valve in my photo?

Yes

any idea where that hose (off of the T fitting from the PAIR valve) goes in my sketch?

To the other PAIR (air suction) valve.

The emissions systems are covered at the end of chapter 1.

 

[claytonia]

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.

Thanks again for all the help - sorry if I wasted your time. Looks like I need to start searching for this air leak elsewhere. If that's even the problem.

 

[claytonia]

yes, that's what I've been saying all along in this thread.

here's the service manual page that confirms it



that's the only hose connected to the #3 cylinder, so if the petcock is permanently removed, that's the line that you must plug. It sounds like you've done that, so you've done everything that needs to be done.

Regarding a possible vacuum leak, any chance that one of your 4 plugged vacuum lines has either a split in the hose, or a leak in the plug?

OK I see that - must have done it when I synched the carbs, if it's in the manual (I have the factory one). My memory has gotten pretty poor. I apologize - this is what you all have been saying all along, and I obviously didn't understand, until now. This explains why I was confused. And yes, time to start examining those hoses - as it really runs like it has a leak. But that may not be it. Almost reached the point of taking it to a shop (oh no, not that!), or selling it as-is. Which would be a shame because it's only got 40k miles, new Delkevic exhaust system, near perfect body work, etc. Beautiful bike. But this problem is sucking up a LOT of time...

THANKS AGAIN!

 

[Andrew Shadow]

To help find a vacuum leak, try propane enrichment. With the engine running, poke around with an unlit propane torch with the valve open just a touch. Anywhere that there is a vacuum leak will suck propane in and cause the RPM to increase. Propane is heavier than air which helps to prevent keeping the propane from being sucked in through the carburetors. Nonetheless, try to keep it away from the carburetor inlets so you don't get an RPM increase through the carbs. Depending on which propane torch head you have, sometimes you can unscrew the air mixer head and put a vacuum hose directly on to the pipe coming up from the valve. This allows you be much more precise where you apply the propane making it easier to locate any vacuum leaks.

Below photo is of a manufactured propane enrichment adapter sold for this purpose. It will give you the idea.

 

[John OoSTerhuis]

if it's in the manual (I have the factory one).

You’ve had the service manual all along….?

 

[tosaw]

The blue circles are the two caps, the yellow circle connects to the fuel valve.

 

[claytonia]

You’ve had the service manual all along….?

Yes, guilty. But the page that shows this being the hose from the #3 carb is under carb synchronization - I looked at the carb. and fuel and related sections. Again, I apologize. If I'd heard initially that this is where it connects, and "you pull it to synch the carbs" (as I said I don't recall this step) - that's all I was asking, where does it connect (as in "it connects to the #3 intake nipple"), which I realize, yes, this was in essence the answers I got. Sorry I didn't get it in the first place.

But I've already taken way too much of your time.

 

[claytonia]

The blue circles are the two caps, the yellow circle connects to the fuel valve.

Yes, thank you - this photo was all I needed.

 

[claytonia]

To help find a vacuum leak, try propane enrichment. With the engine running, poke around with an unlit propane torch with the valve open just a touch. Anywhere that there is a vacuum leak will suck propane in and cause the RPM to increase. Propane is heavier than air which helps to prevent keeping the propane from being sucked in through the carburetors. Nonetheless, try to keep it away from the carburetor inlets so you don't get an RPM increase through the carbs. Depending on which propane torch head you have, sometimes you can unscrew the air mixer head and put a vacuum hose directly on to the pipe coming up from the valve. This allows you be much more precise where you apply the propane making it easier to locate any vacuum leaks.

Below photo is of a manufactured propane enrichment adapter sold for this purpose. It will give you the idea.

Thanks so much for this tip Andrew - I may resort to this.

 

[dwalby]

Thanks so much for this tip Andrew - I may resort to this.

spraying carb cleaner in the general area will also work similar to the propane method.

 

[John OoSTerhuis]

Check the engine troubleshooting section. I know of one case where a leak in the exhaust was the problem. Another possible culprit are the carbs’ air-cut valves.

 

[claytonia]

spraying carb cleaner in the general area will also work similar to the propane method.

Thanks, I will try the carb cleaner - it's a bit more manageable in size. I have both, although no hose for my propane tank.

 

[claytonia]

Check the engine troubleshooting section. I know of one case where a leak in the exhaust was the problem. Another possible culprit are the carbs’ air-cut valves.

OK will do. Thanks again for all your suggestions and tips!

In checking various things on the bike, like spark, I tried something and was surprised at the result: The bike was idling and I went around and pulled each plug cap off one at a time. Didn't get shocked! But also it did not make any difference to the idle - and this is true for every cylinder. I'm just not able to figure out how this is possible.

 

[Rex Beard]

I'm working on my fuel shut off valve and am interested in why some say you can run without it ?????

 

[rwthomas1]

I'm working on my fuel shut off valve and am interested in why some say you can run without it ?????

There are lots of posts on this. Some remove the shutoff valve entirely. Others rebuild it. The valve is vacuum actuated so when the engine is started (on the fuel remaining in the carburetor bowls), the valve opens and fuel begins to flow. Shutdown the engine, no vacuum, and the valve closes shutting off the fuel. The ST1100 has a low pressure fuel pump that is really only needed when the fuel level drops below half a tank. So it will gravity feed from the halfway point up and if a carburetor needle was to get hung up then fuel would overflow out of the carb bowl breather ports, and also into the intake of the affected cylinder. This would be a very rare occurrence, but the shutoff valve is there to make sure this doesn't happen. The more common occurrence is the shutoff valve diaphragm fails and it leaks gas at that point. Removing it you run the risk, albeit very small, that the carb needles will not do their job at some point. Many here have removed/bypassed the shutoff, including myself, and have never had a problem.

Back in the "good ole days" the manual fuel valve (petcock) that could be simply turned on and off. I much prefer that option as I know what I did, and did not do. Back then some riders shutoff the fuel every time they stopped. Others forgot the valve existed until they needed to service the carbs. Either way, I can only remember one instance of a carb needle leaking and the carbs just needed a rebuild. Its up to you how you wish to proceed.