pair system on '91

[mtflyr]

I need some advice.

Is it recommended to remove the pair system from a '91 1100 with 52,000mi. or keep it intact?
I did send this once before, but, would like try to get a bit more feedback. I do have the area already exposed as I am replacing the carb. insulators which are in transit. So, now would be the time...

Any advice would be appreciated. Thanks

 

[DeanR]

I'm gonna have to decide on that shortly too. I'll likely keep it because I figure the Honda engineers are generally pretty smart.

 

[mtflyr]

Yes, I would agree. But, when it comes to emissions they are drawn away from what is best for the engine and have to follow a different set of rules. I am still under the belief, for the most part, simple is always better. Even with that said, I am still questioning, but, leaning toward removing it.

 

[DeanR]

Yes, I would agree. But, when it comes to emissions they are drawn away from what is best for the engine and have to follow a different set of rules. I am still under the belief, for the most part, simple is always better. Even with that said, I am still questioning, but, leaning toward removing it.

And I absolutely agree with you too..

 

[Rick Gibson]

Welcome to ST-Owners.

 

[sirepair]

Pulled mine off several years ago, no adverse effects. Now there's 10lbs of stuff in a box in the garage and the bike is just a little lighter!!! I figure that even without the air pump, I'm putting less "crap" in the air then when I drive my Suburban... And now there are fewer things to go wrong with the bike.

I made my own block off plates too.

 

[mtflyr]

Sound good. I too plan to make my own plates. Can you tell me are there any subtleties to be aware of, i.e. gaskets on the plates, carb. readjusting, potential exhaust leaks, etc.?

 

[ST1100Y]

I'll likely keep it because I figure the Honda engineers are generally pretty smart.

+1... I decide by the fact if there are leaks; if the pump diaphragms are OK, leave it alone. But if there definite leaks to determine, remove it (would be too expensive to repair)
I put a small tube on the vacuum sided stub of the pair pumps, other end between my lips, suck vacuum and plug the end of the tube with tip of tongue. If it 'holds' all fine, if it draws air obviously its leaking... which messes up carb sync and mixture...

 

[John OoSTerhuis]

It is recommended to 'leave it intact.' The air suction valves have no effect on performance and they reduce emissions. It is a simple, robust system. I know of no verified actual failures, just rationalizations for removal. The service manual has a very simple and clear inspection procedure. Never heard of any ST1100 failing that. Do what you want but there's no good reason to remove a functioning, USA mandated system. Of course, that's just my humble opinion.

Regards, John

 

[mtflyr]

Well, I jumped. The system is removed.

With that said, I understand its function, however, I don't necessarily buy into it being something more "efficient" or better for the engine/enviroment whether it is US mandated or not.

 

[ST1100Y]

Never heard of any ST1100 failing that.

Well, on the old '94 ST I'd just refurbed, one (the portside) PAIR pump diaphragm was leaking... so I decided to remove the assembly and to properly plug all now unused plumbing (despite the fact that I'll violate emission regs with that...) On the other '00 ST I'll leave the PAIR alone as long as it doesn't give any problems. Would need to have emission tests performed to document any differences there, the limited human sense of smell seems not able to distinguish them two bike's emissions... There are rumors about the manifolds/downpipes running cooler with the PAIR installed, OTOH wouldn't the 'after oxidation' of exhaust gases due the supplied oxygen not actually raise the temps there?

 

[John OoSTerhuis]

Thanks for the report, Martin. Were you having any symptoms that caused you to suspect a problem with the air suction valve? Any guess as to why the diaphragm was damaged/leaking... contaminate like carb cleaner?

BTW folks, there's no actual pumping going on in this system, and Honda designed and installed it to pass emissions standards, so it does in fact measurably do something good.

John

 

[ST1100Y]

Were you having any symptoms that caused you to suspect a problem with the air suction valve?

Faced some issues during carb syncing John, rough & unstable tickover... Since the bike was in storage for ~2 years, we'd figured to pull the carbs and check everything while at it... methinks the diaphragms will eventually fail one day due the mechanical wear on them, just as the one in the fuel petcock...

 

[John OoSTerhuis]

Faced some issues during carb syncing John, rough & unstable tickover... Since the bike was in storage for ~2 years, we'd figured to pull the carbs and check everything while at it... methinks the diaphragms will eventually fail one day due the mechanical wear on them, just as the one in the fuel petcock...

Thanks, Martin. I see now that #2 and #4 could be affected during a sync if one or both air suction valves' diaphragms were torn. I just had my carbs off to replace coolant hoses and elbows. Pulled the cover on one of my valves and its 22 year old diaphragm looked (and still works) fine.

Thanks again. Two more data points in ST1100 maintenance history.

BeST, John

 

[ST1100Y]

Pulled the cover on one of my valves and its 22 year old diaphragm looked (and still works) fine.

Easier/less efforts to simply place a small hose on the relevant stub, draw vacuum and see if it holds; after having to find that a small hole in the fuel petcock is not found by motorcycle mechanics, but rather 'compensated' by messing with the sync setting on #3 instead, I added this procedure for all 3 items in question to my scheduled service work now... I have yet not located a repair kit for those PAIR things, only the complete pumps are avail (P/N 18610-MT3-730 (port) & 18620-MT3-730 (starboard side), secondary air injection control valve), but maybe the collective wisdom brings up a suitable spare for those diaphragms in there.