PAIR removal

[thekaz]

Just for discussion sake... Does the ST1300 also have a pair valve system? I know that both my VTX 1300 which is carbuerated and my VTX1800 which is fuel injected have the pair systems. I guess I never really dug into an ST1300 enough to think about it. The ST1300 already runs so powerful, smooth, and thrifty. I don't want to disturb it

Also for discussion sake I can't believe all the differing ideas as to what it is there for on the engine. Per my reading other sources years ago the function is to allow air into the exhaust right after exhaust valve to facilitate final ignition for any unburned fuel vapor that may be escaping the motor when you let off the throttle, thereby helping emmissions. That's where the popping can come from during deceleration. The increased vacuum when you close the throttle opens the reed valves allowing all this to take place. It's been a few years since I read all about it. Sounded similar or like a fancy EGR system found on automobiles. Did I read all of this wrong? Removing it from my VTX twin machines offered a little less popping during deceleration and cleaned up the top of the motor a great deal, but it offered no difference in fuel mileage or performance. It was simply less "stuff" to troubleshoot. The cover plates are still available for those machines at many sources.

The ST1300 does have a air injection system which like others introduces oxygen in the exhaust to "continue" the combustion process in the exhaust pipe. This in turn raises the exhaust temperature to increase the efficiency of the "cats". The ST1300 is a closed loop system so removing the cats & air system will not effect the final air fuel mixture. My personal experience is that removing the cats & air system resulted in no noticeable performance gains but a HUGE difference in heat )
I did it because of my understanding that emissions and fuel efficiency are not the graphical curve, so I was hoping for some gains in mileage. Still pretty dam happy with less heat, weight and giving David Suzuki nightmares LOL

EGRs will plumb exhaust gas back into the intake manifold at the appropriate times to help the reduction of NOX

 

[John OoSTerhuis]

Here's the ST1100 Archive Of Wisdom article that you must have missed during your search:
PAIR Removal ( ST1100 )
http://www.st-riders.net/index.php?topic=10280

Edit: I respectfully disagree with my friend, Adam Frymoyer in his AOW article (link above), about the probability of the ST1100 PAIR components deteriorating and failing. I cleaned the stuff off my PAIRs' diaphragms 120K miles ago, still working fine; and my original, 25 y/o, PAIR vacuum hose (all ~10" of it) looked just fine the other day. But if your little section of PAIR vacuum hose is bad, then you'd better also replace all four of your intake manifold port hoses (of the same age) that you use to sync your carbs.

 

[John OoSTerhuis]

The increased vacuum when you close the throttle opens the reed valves allowing all this [air to exhaust manifold] to take place.

Exactly backwards! And it's not the reed valves, it's the air suction valves (also called Air Injection Control Valves by Honda) that CLOSE at throttle-roll off (high intake manifold vacuum), cutting off the flow of air to the exhaust manifold, thereby preventing afterburn. But increasing emissions. Please read the Honda Service Manual(s).

The separate reed valves inside the PAIR housings prevent reverse air flow during positive pressure pulses in the exhaust system.

The "PAIR valves" allow continuous passage of filtered air to the exhaust manifold to help burn off unburned hydrocarbons, lowering emissions. All the time during normal operation; except when they CUT OFF this AIR FLOW during high intake manifold vacuum (increased emissions during this time).

All PAIRs operate this way. They are not "anti-smog pumps" like used on cages.

John

 

[rupp]

John, Thanks for your reply. What got me checking it out is I have the carbs removed and thought now is a good time. I don't think I'll do it seems to just be more work. Neil

 

[John OoSTerhuis]

P.S. In the 18+ years I've been on the forums I know of only one documented case of an air suction valve failure (rubber diaphragm tear - Austria). If you have some popping during deceleration/engine braking that's pretty common. I've always called it "decel burble." If you remove a functioning PAIR system you'll still have the same burble/popping afterwards! No outside air into the exhaust manifold either way!!

Anyone that claims they've eliminated (or more likely only 'reduced') their ST1100's decel popping by removing their Secondary Air Supply System is frankly fooling themselves.

The PAIRs are so simple to confirm that they're OK and NOT malfunctioning, that it's ridiculous! The test is on page 5-17 in my Honda Service Manual. Engine off, a short length of hose and a MityVac. The MityVac isn't really even needed, just suck on the hose with your mouth. If the vacuum holds they're good.

If a PAIR would actually fail you'd have more problems than just decel popping, you'd more than likely not be able to sync the carbs...

I've said it before and I'll say it again, every time - if you want to remove the PAIRs, just do it; without rationalizing it, especially if you're basing your actions on erroneous information. And please, don't perpetuate false technical descriptions of systems operations/functioning.

John

 

[John OoSTerhuis]

P.P.S. If your PAIRs check out OK and you still think you have an afterburn problem, the service manual troubleshooting guide also lists:
- too lean mixture in slow circuit
- air cut-off valve malfunction
- vacuum hose leaks

You'll have to remove the carbs to inspect the air cut-off valves. See the Honda Common Service Manual, p.8-7 and p.8-14; also, Adam Frymoyer's most excellent carb rebuild article in the ST1100 AOW.

Besides any vacuum hose leak, a lose manifold or hole in the exhaust/muffler system can add unwanted air when there's raw, excess unburned fuel ('hydrocarbons') in the exhaust manifold. I have heard of two such cases.

OK.... I think I'm done now.

John