Who understands the PAIR system to know I can clamp it off, leaving it in place?

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I installed an Audiovox cruise control recently and while it will maintain speed less than 55mph, if I try to set it on the interstate, it doesn't seem to be able to last more than 3 or 4 seconds, pointing to it's inability to maintain the vacuum. I have a pvc canister made, but if there's a leak, it won't matter.
What I want to do is clamp off the "T" connection of tubing between the 4th and 2nd cylinder, isolating my connection instead of the "T" connction, to use the 4th cylinder vacuum with a new vac hose where I believe the leak is coming from. Any probably with this? I know a lot of guys just remove the PAIR tubing and plug it off permanently.
 
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Lots of opinions on this (PAIR removal) but here's a good write-up on removing it... http://www.st-riders.net/index.php?topic=10280.0
Thanks for the link. It is likely the next time my carbs are out I will remove and plug them off at that time. When I made a "T" connection for the supply of vacuum to the cruise control, I am relying on the rest of the PAIR systems integrity to hold a vacuum.
I would like to put a clamp where the green line is and attach a new vacuum line to cylinder 4. Rubber degradation could be the cause of this leak, but I can isolate the issue if cylinder 2 and PAIR is removed from the equation. It's probably not going to hurt, especially if it were only short term to determine the source of fault with the cruise control.
PAIR.jpg
 
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I see no mention of a valve inserted between the reservoir and carb.. this allows the vacuum to be stored ,via the resv., to be used as required. the valve is easy to install backwards so take care to check out for proper flow before calling it good. most home hobbyists use a smog valve from the local parts houses.- often replaced as preventative maintenance.
 
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I see no mention of a valve inserted between the reservoir and carb.. this allows the vacuum to be stored ,via the resv., to be used as required. the valve is easy to install backwards so take care to check out for proper flow before calling it good. most home hobbyists use a smog valve from the local parts houses.- often replaced as preventative maintenance.
Don't mean to be elusive as to the care in this entire operation. It probably took me 12 hours. To stay to the point, where the green line is, in my previous diagram, I inserted a "T" fitting that goes to the one way valve then that goes to another "T" fitting for the vac container and cruise control mechanism. It does work properly at slower speed, 55mph, but not faster. I don't want to say I wasn't careful enough to make sure the vac had no leaks, I wanted to see if it was sufficient before further intervention. Well, after testing, it doesn't work...yet.
The further intervention is, because the PAIR is still in place, to clamp off the vac that would normally pull from the 2nd and 4th cylinder and only connect the 4th cylinder to system for cruise control. I know I'm being redundant in my explanation from further posts, it is likely a test of clamping the line and connecting the 4th cylinder alone is the next likely step. We all wish we'd done things before, but when I had the carbs off and coolant hoses to redo would have been a great time to pull the PAIR. I didn't because I wasn't setup to plug it off, so I kept driving on.
 
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+ 1 on the 1-way in-line vacuum valve to keep reservoir "in-vacuum".
My theory is, a good enough leak of my potential vacuum is being lost in my present configuration. Something I haven't mentioned, this temporary bypass would prevent me from having to remove and plug the PAIR system in order to have the soonest answer to the integrity of my vacuum reservoir. It would seem that I have enough vacuum to hold the throttle at 55mph or less, no creating the necessary vacuum for the capacity of the reservoir design. A small leak unnoticeable for lower requirements of vacuum. It sucks.
 

John OoSTerhuis

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It's dead simple to check if the PAIR hoses and valves are the source of a vacuum leak. Disconnect the PAIR hose from the T between the #2 and #4 intake manifold hoses, and apply vacuum (360 mmHg/14.2 inHg) to it with a Mityvac (or even just your mouth). If it holds then that's not the source. Page 5-17 in the Service Manual. This test also should be conducted before anyone rationalizes their removal by claiming the PAIR system is the cause of any "backfiring" (afterburn).

FWIW

John
 
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It's dead simple to check if the PAIR hoses and valves are the source of a vacuum leak. Disconnect the PAIR hose from the T between the #2 and #4 intake manifold hoses, and apply vacuum (360 mmHg/14.2 inHg) to it with a Mityvac (or even just your mouth). If it holds then that's not the source. Page 5-17 in the Service Manual. This test also should be conducted before anyone rationalizes their removal by claiming the PAIR system is the cause of any "backfiring" (afterburn).

FWIW

John
I remember the seal to the original "T" connection not being very good. I made a mental note if there were any problems to come back to that because it could have been good enough. Knowing the cylinders are pulling a vacuum while the engine is running, with a one way valve in place, still doesn't seem to be a good enough vacuum. It's still early. It's the first ride after installation. I've checked all the switches, 1 and 7 are on, the rest are off. My vac canister is 8 inches long from 1 1/2 inch pvc, this could be the culprit of a leak. It may not even be a leak, it's all hypothesis. When I get a chance to go exploring again, I will be looking for the obvious thing, then start working on the deductive thing. I'm miles ahead of it not working at all. My very first ride about 55 it worked and held speed, disconnected when the clutch or brake handle was depressed and every other function like it's supposed to, just not any faster than 55 for right now. Another behavior it has when a resume, while testing it, it's a hard acceleration with a lurch, like a horse taking off abruptly. Don't know what that's about but that symptom could go away when I find the underlying issue.
 

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Did you check the canister for leaks before installing?

How accessible is your vac. canister? Can you pull it out and test it? Apply a vacuum or pressure to it and put it under water. If you pressurize it and it bubbles, obviously a leaker. Draw a vacuum on it and submerse it. Pull it out and check for water inside the canister. If it's dry, move on to the bike system.
 
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Did you check the canister for leaks before installing?

How accessible is your vac. canister? Can you pull it out and test it? Apply a vacuum or pressure to it and put it under water. If you pressurize it and it bubbles, obviously a leaker. Draw a vacuum on it and submerse it. Pull it out and check for water inside the canister. If it's dry, move on to the bike system.
I appreciate the feedback I'm getting. The canister is accessible and made of pvc so hopefully it won't suffer damage from submerging it. I will also clamp off the line to segregate the vacuum source to the PAIR system from cylinder 4. Will get to it tomorrow. I hope there will be no bubbles and the new vac line connection drives it home. Oh yeah, haven't forgotten to test the PAIR integrity with a vacuum test as well.
 

John OoSTerhuis

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Hmmmm.... your servo cable is fully withdrawn but the throttle bellcrank has only been rotated to the point that gives 55mph in fifth gear(?) Just thinking out loud here... maybe you need a longer lever on the bellcrank, or should position the servo cable sheath anchor point further away from the bellcrank. Maybe...
 
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I made sure when I secured the servo cable to be completely extended to give the maximum pull for acceleration adjustment. IF, my checks for PAIR, vac container and 4th carb connection for function don't work, I will likely route the servo cable the way you did, unseating the carbs, drilling and tapping and all of that. So, hoping for the best.
I will also admit where I have connected to the throttle linkage it doesn't move a minimum of 4 cm. It could decide it's having to pull "too hard" to maintain speed, which is why other installs that have worked aren't like mine. I primarily followed your install and Fred Adkins found at this URL http://will.mylanders.com/mc/st1100/audiovox/
The only difference for an articulation point than Fred's was the pulley. Having just looked at his picture again, I've noticed his design allows more leverage than mine may be capable of. I like the idea of the pulley, but there is no aid in leverage. If it's too hard on the servo to pull, there may not be an issue with my vacuum at all. The failure could be the unit having to work to hard and releasing. We'll see, I've got some things to verify tomorrow before I jack around with
 
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I've just realized I may not have to completely scrap my design, and attach an arm to the bell crank. I can attach the arm to my pulley and make two points of contact for a greater advantage of leverage. It's possible the servo cable only moves 1/8 to 3/16 to manage speed, so I get the importance of the best leverage, not just to make the connection. I have until June 11th to get it working, my incentive is to use it for a 2500 mile trip over 10 days. I'm very close.
 
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Oh and John, how did you seal your control. I used permatex on the back, what did you use to keep the weather out.
 

John OoSTerhuis

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Oh and John, how did you seal your control. I used permatex on the back, what did you use to keep the weather out.
Surprisingly, it stays pretty dry mounted behind the left tip-over bar, but I sealed the servo with common clear RTV.

I sent a reply to your email.

John
 
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John, I disconnected my one-way valve and tested the integrity of the PAIR system by sucking on it expecting it to be closed and almost died from it. It was disgusting and no vacuum. This is with the engine off.
Additionally, in a previous conversation about throttle travel while in cruise control, I meant there isn't as much travel in the throttle for the power. As you well know owning an ST1100 a long time you really don't roll on the throttle really hard. I could be mistaken and I also live in flat country in Indiana. I'm guessing with a longer hill climb your throttle could move half an inch of travel?
I'm on it again and have the tupperware off. I'm exploring how to reattach cables to get a better pulll of torque. Will be looking for updates.
 
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