pair system?

I took mine out but kept all the parts and if I’m in there again, I think I will put it back. Cleaned it up, there was a canister that had a thick oily substance that I cleaned up. I thought it would stop some of the “gurgling “ and popping when decelerating but nothing changed.
 
Sunday Rider said:
I took mine out but kept all the parts and if I’m in there again, I think I will put it back. Cleaned it up, there was a canister that had a thick oily substance that I cleaned up. I thought it would stop some of the “gurgling “ and popping when decelerating but nothing changed.
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Verify system actually works. Most people definitely report changes under deceleration when removing.
 
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roadrider said:
What is it's function?
What effects will occur if system is removed?
Who has removed Pair and what was the results?
Ride Safe
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Function: reduces polution. Description and schematic in Chapt 1 of the Honda Service Manual
The system is passive and there is no effect on performance before or after removal. Many have removed it in the misguided attempt to reduce perceived ‘after burn‘ - it doesn’t. No noticeable change, just increased pollution. All ST1100s exhibit ‘decel burble’ to some degree during high rpm throttle roll off, as do all motorcycles without a PAIR system. The ST1100 PAIR system is pretty much bullet-proof. The test to see if it’s working is dead simple, IIRC chapt 5 in the manual. JMNSHO

John
 
Yeah, the only time it kicks in is when coasting with closed throttle. It doesn’t affect bike’s operation under any other conditions.

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I removed the PAIR valves and plumbing on my 1991 but retained the chrome tubing....looks nice. I plugged the tubing ends with rubber tube sections, short shouldered bolts and hose clamps. Replaced the gaskets at the heads, Part #14 four of them, with blanks I made from gasket material. No difference noticeable at all in performance.
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Ditto...
The '00 has the PAIR system, removed it on the '94... absolutely no difference in performance... despite rumor telling a 2 HP gain without it...
(except the PAIR tech complaining that both are running too lean... in real both are set to 2 1/2 rotations out instead the 2 1/8 given for the AR (Austrian) code...)
 
ST1100Y said:
(except the PAIR tech complaining that both are running too lean... in real both are set to 2 1/2 rotations out instead the 2 1/8 given for the AR (Austrian) code...)
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Aren't the adjusters air-screws rather than fuel-screws, meaning that open farther does lean the mixture?
 
roadrider said:
Thank you, all Another question, What is the purpose of the rubber diaper under the carbs? Is it needed? Ride Safe
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Methinks its an air-guide, shielding the carbs(bowls) from the engine heat...
I ran with and without it, can't tell a difference... but(!) I'm also running two air-ducts instead of only one, providing more cool/ambient air to the intake at the aft of the air-box...
(while having only one, I did experience vapor lock after idling at a red light in the summer... with two snorkels this issue vanishes...)
 
There is another system that works in conjunction with the pair system that really effects the deceleration burble and backfire, It is built into the carb bodies. I don't have a manual in front of me right now but it uses small triangular diaphragms and when the throttle is closed and intake vacuum peaks, it shuts off the fuel flow through the jet system. When I had my ST1100 it was starting to burble and backfire quite a bit and thinking that it was the pair system I disabled it. That helped a little bit, but it did not stop the problem, so I rebuilt the carbs and replaced the diaphragms and springs on this vacuum fuel cutoff system and all burbling and backfiring stopped completely. I bought a complete kit with the diaphragms and springs for this from some aftermarket house, it's been so long I don't remember where I got it.
 
Dan, I think you’re referring to the air-cut valves, but they’re not triangular. If the PAIRs pass the function check in the manual, the troubleshooting instructions then point to the air-cut valves as a possible source. Did you perform the check on your PAIRs system before removing them? If they didn’t pass, did you take the air suction valves apart and inspect the diaphragms? How’d they look? Just curious…

John
 
roadrider said:
What is it's function?
What effects will occur if system is removed?
Who has removed Pair and what was the results?
Ride Safe
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I removed mine over 10 years ago. I left the chrome piping at the exhaust header (Chrome looks good) and replaced with an exhaust worthy gasket to seal the tube. This way I did not have to worry about future leaks. I agree the purpose is to improve emissions, I'm not sure that can be proven!
 
John OoSTerhuis said:
Dan, I think you’re referring to the air-cut valves, but they’re not triangular. If the PAIRs pass the function check in the manual, the troubleshooting instructions then point to the air-cut valves as a possible source. Did you perform the check on your PAIRs system before removing them? If they didn’t pass, did you take the air suction valves apart and inspect the diaphragms? How’d they look? Just curious…

John
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You are probably right about the shape of the diaphragms - It has been quite a few years ago when I replaced them and I've rebuilt many different kinds carbs since then.

At the time I just blocked off the pair ports to see how it ran without them. I wasn't in search of any power improvement at the time but just was trying to reduce the deceleration popping etc.. That popping was pretty annoying especially being I had installed Delkevic mufflers and the popping was louder than with stock mufflers. After that I removed the pair piping altogether mainly just to simplify access etc. If I remember correctly some of the hoses were degraded pretty badly that connected to the chrome pair piping.
As far as performance - the pair system has no effect on the running of the engine as you and others have said. All it does is introduce air into the exhaust ports to allow complete burn of unburned fuel in the exhaust. The air-cut system probably has more to with keeping the exhaust clean than anything - there was a huge reduction with engine burbling and popping during deceleration after replacing the air-cut diaphragms and springs. I am assuming this was because the fuel was cut off when the throttle was closed so the unburned fuel was not igniting in the exhaust header during deceleration.
 
bdalameda said:
You are probably right about the shape of the diaphragms - It has been quite a few years ago when I replaced them and I've rebuilt many different kinds carbs since then.

At the time I just blocked off the pair ports to see how it ran without them. I wasn't in search of any power improvement at the time but just was trying to reduce the deceleration popping etc.. That popping was pretty annoying especially being I had installed Delkevic mufflers and the popping was louder than with stock mufflers. After that I removed the pair piping altogether mainly just to simplify access etc. If I remember correctly some of the hoses were degraded pretty badly that connected to the chrome pair piping.
As far as performance - the pair system has no effect on the running of the engine as you and others have said. All it does is introduce air into the exhaust ports to allow complete burn of unburned fuel in the exhaust. The air-cut system probably has more to with keeping the exhaust clean than anything - there was a huge reduction with engine burbling and popping during deceleration after replacing the air-cut diaphragms and springs. I am assuming this was because the fuel was cut off when the throttle was closed so the unburned fuel was not igniting in the exhaust header during deceleration.
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That’s why I removed 2-Bros mufflers on my bike. The deceleration popping was too annoying. That and louder volume was more than I wanted.
 
DannoXYZ said:
That’s why I removed 2-Bros mufflers on my bike. The deceleration popping was too annoying. That and louder volume was more than I wanted.
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After installing the Delkevic mufflers I too found them to be too loud. I found out that Delkevic made quiet inserts for the mufflers which I installed. Those inserts made the sound very tolerable and very slightly louder than stock with a deep tone that was just fine. The weight difference between the Delkevic and stock mufflers was huge.
 
bdalameda said:
There is another system that works in conjunction with the pair system that really effects the deceleration burble and backfire, It is built into the carb bodies. I don't have a manual in front of me right now but it uses small triangular diaphragms and when the throttle is closed and intake vacuum peaks, it shuts off the fuel flow through the jet system. When I had my ST1100 it was starting to burble and backfire quite a bit and thinking that it was the pair system I disabled it. That helped a little bit, but it did not stop the problem, so I rebuilt the carbs and replaced the diaphragms and springs on this vacuum fuel cutoff system and all burbling and backfiring stopped completely. I bought a complete kit with the diaphragms and springs for this from some aftermarket house, it's been so long I don't remember where I got it.
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It doesn't shut off the fuel flow, it shuts off the air flow, thus richening the mixture so that it will burn in the cylinder instead of the exhaust.
 
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