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

  1. #1
    David moddy's Avatar
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    Who understands the PAIR system to know I can clamp it off, leaving it in place?

    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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  3. #2
    Site Supporter paulcb's Avatar
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    Re: Who understands the PAIR system to know I can clamp it off, leaving it in place?

    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

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  4. #3
    David
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    Re: Who understands the PAIR system to know I can clamp it off, leaving it in place?

    Quote Originally Posted by paulcb View Post
    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.
    Click image for larger version. 

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  5. #4

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

    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.

  6. #5
    David
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    Re: Who understands the PAIR system to know I can clamp it off, leaving it in place?

    Quote Originally Posted by the_gr8t_waldo View Post
    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.
    Last edited by moddy; 05-24-2017 at 11:00 AM.

  7. #6
    TourNut's Avatar
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    Re: Who understands the PAIR system to know I can clamp it off, leaving it in place?

    + 1 on the 1-way in-line vacuum valve to keep reservoir "in-vacuum".

  8. #7
    David
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    Re: Who understands the PAIR system to know I can clamp it off, leaving it in place?

    Quote Originally Posted by TourNut View Post
    + 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.

  9. #8
    Life Is Good! John OoSTerhuis's Avatar
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    Re: Who understands the PAIR system to know I can clamp it off, leaving it in place?

    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).

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

    Quote Originally Posted by John OoSTerhuis View Post
    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.

  11. #10
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    Re: Who understands the PAIR system to know I can clamp it off, leaving it in place?

    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.
    "Nothing screams bad craftsmanship like wrinkles in your duct tape."

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