Air Chamber/ Duct Assembly - Why is there a screw in this hose?

WillemVanKatwijk · Monday at 5:27 PM

Hi all,

I was working on the bike of a neighbor (Honda ST1100S) and because the bike won't start after a long period of standing idle in a shed (of garage as we call that here in The Netherlands) I was removing the carbs for inspecting and cleaning. When I removed the air chamber / duct assembly I noticed, when removing the tube attached to the air chamber, a big screw inside the tube. Now, as this tube is connecting to the engine I'm wondering why there is a big screw pushed into that tube (or hose)? Why would a manufacturer push a screw into that hose? I think it's a vacuum hose, but I'm not sure and also I'm not sure why the screw is inserted? It's very hard to get the screw out of the hose and I think it's cheaper to replace the hose. But .... I can't find the hose on any of the pictures in the manuals. As yoiu are all very knowledgeble people I'm requesting your help to identify the purpose of the screw in the hose and what if I replace the hose with no screw in it (or remove the screw)? Please check the attached picture. Thanks!

Uncle Phil · Monday at 5:51 PM

That ain't factory - somebody before you put the screw in there.

Pulling the entire carb 'set' off is not a big deal.
You have to loosen the 2 carb insulator brackets beneath each carb.
Then you gently pry upward with a broom handle or a hammer handle and they pop off.
It is easier if you remove the gas tank first as it gives you a lot more working room (beware of the tank connector buried on the left side - red connector).

WillemVanKatwijk · Monday at 5:59 PM

Uncle Phil said:
That ain't factory - somebody before you put the screw in there.

Aha! Thanks. Now I know it's not factory (Yes, I believe you Uncle Phil!) can you shed a light on the purpose of this screw insert? Is this to solve another (hidden) issue? I just can't imagine that a dealership (or someone else) pushes a screw in a hose, just for fun ...

There must be a reason and since I can't find the purpose of that hose (I think it is a vacuum hose) it's hard for me to understand the purpose of the screw.

Uncle Phil · Monday at 6:02 PM

Obviously it is to block off that vacuum line since it is clamped.
With carb mat in place, it's hard to tell what it should be going to.
Plus on this side of the pond we have the 'Pair' system which has a bunch of plumbing and hoses around the carbs.

SMSW · Monday at 7:00 PM

That is a common way of blocking off a vacuum hose when the (shade tree)* mechanic is too lazy to remove the hose and block it at the source.

*Term describing a do it yourself mechanic

Bikeric · Monday at 8:26 PM

Could it be a hose that went to the vacuum operated fuel valve that someone has removed, or bypassed, a common practice on ST1100s when they stop working properly.? You then have to blank off the hose, usually with a 6mm screw or bolt.

Al st1100 · Monday at 8:36 PM

Bikeric said:
Could it be a hose that went to the vacuum operated fuel valve that someone has removed, or bypassed, a common practice on ST1100s when they stop working properly.? You then have to blank off the hose, usually with a 6mm screw or bolt.

no

WillemVanKatwijk said:
Hi all,

I was working on the bike of a neighbor (Honda ST1100S) and because the bike won't start after a long period of standing idle in a shed (of garage as we call that here in The Netherlands) I was removing the carbs for inspecting and cleaning. When I removed the air chamber / duct assembly I noticed, when removing the tube attached to the air chamber, a big screw inside the tube. Now, as this tube is connecting to the engine I'm wondering why there is a big screw pushed into that tube (or hose)? Why would a manufacturer push a screw into that hose? I think it's a vacuum hose, but I'm not sure and also I'm not sure why the screw is inserted? It's very hard to get the screw out of the hose and I think it's cheaper to replace the hose. But .... I can't find the hose on any of the pictures in the manuals. As yoiu are all very knowledgeble people I'm requesting your help to identify the purpose of the screw in the hose and what if I replace the hose with no screw in it (or remove the screw)? Please check the attached picture. Thanks!

need the year of the bike, makes a difference. does t still have pair valves?

ST1100Y · Tuesday at 1:58 AM

Al st1100 said:
need the year of the bike, makes a difference. does t still have pair valves?

He wrote ST1100S, which would ID it as a '95...
PAIR was present in all EC spec models from '91/'92 onward...

Unless its an import I assume this fiche will cover it:

Honda ST1100A PANEUROPEAN 1995 (S) EUROPEAN DIRECT SALES parts lists and schematics

✓ ST1100A PANEUROPEAN 1995 (S) EUROPEAN DIRECT SALES parts lists and schematics ✓ Easy repairs with Honda diagrams ✓ Free access!

www.cmsnl.com

Likely someone attempted to disable the PAIR system over a vacuum leak, hence plugged that hose...

WillemVanKatwijk · Tuesday at 8:00 AM

Yes I can confirm that the PAIR system is on this bike. So, that leaves me to think that PAIR system can be:

1. Left alone and leave it as is;
2. Check if the PAIR system can be repaired (are the valves available in EU?);
3. Remove the complete PAIR system;

If 3 is chosen, do I just cutoff and close the valves?

Simple question: what is the best way to progress? I'm tempting to choose option 1.
Thanks for your advice!

Uncle Phil · Tuesday at 8:14 AM

Probably easier to remove the PAIR than try to repair it.
You will need blocking plates for where the metal chrome 'pipes' go into the head near the exhaust.
Here's a link that might be of help to you -

ST1100 Pair Removal

koczarski.com

ST1100Y · Tuesday at 8:15 AM

1. only if all diaphragms are still airtight (re: vacuum leak)
2. AFAIK not serviceable; source used replacements from eBay or breakers
3. eliminate vacuum tube from carbs, their air-supply from the filter-box plus install blocking plates at the head ports (loc 14 in above fiche)

Al st1100 · Tuesday at 9:16 AM

Pair valves are not going to cause a running problem but , for now seal that hose better. Screws in vacuum hoses leak thru the treads. There was a myth that you would get better gas mileage, not true. IMO get the bike running properly before adressing the pair valve issue. You don't know what else is wrong. 95 may have the 28 amp alternator so there may be other more important things to do.

Uncle Phil · Tuesday at 9:17 AM

I have 4 'roadworthy' ST1100s - 3 have PAIR and one has PAIR removed (by previous owner).
As far as performance goes, not a bit of difference according to my butt dynamo.

motornut · Tuesday at 11:55 AM

This something that some mechanics believe must be done to any motor vehicle. Remove or disable all emission control, a bit of research as to the operation of the component helps to know what is going to be the outcome.
The one thing that comes to mind is the very old Rotary engine in the very old Mazda, taking off the controls destroys the second rotor, recommendations were not to buy one that has been modified. EGRs are another one, the intent was to introduce inert gas into the combustion chamber to keep the combustion cool, which helps in the early fuel injection since the mapping allows for it. Disconnecting it raises the temp and I have run into it causing detonation in high mileage engines.
Since the map is hard wired into the ECM, you pretty much get a trouble code and not much else

afrymoyer · Tuesday at 6:42 PM

This is the filtered fresh air intake hose for the PAIR system as mentioned above. Being plugged like this, will not create any sort of vacuum leak, or drivability problems. The bolt is only preventing filtered fresh air into the PAIR valves themselves. Even if the bolt/plug were missing, "unfiltered" fresh air would be drawn in and pumped into the exhaust system, without any drivability issues. Personally, if it were my bike, I'd take them out. The carbs are out and everything is exposed. Why not?

I also see that you've removed the upper aluminum carburetor plenum/snorkel assy before removing the carbs (I've seen your other thread). Bad move. You'll never get it back together easily and it will fight you every inch of the way. It'll be virtually impossible to get everything back into alignment and assembled. After you've cleaned and rebuilt the carbs, be sure to re-assemble the entire carb bank before reinstalling (upper plenum/snorkel assy).

Carb Removal and Rebuild ( ST1100 ) *

www.st-riders.net

PAIR Removal ( ST1100 ) *

www.st-riders.net

WillemVanKatwijk · 2024-11-13T01:59:54-0600

afrymoyer said:
This is the filtered fresh air intake hose for the PAIR system as mentioned above. Being plugged like this, will not create any sort of vacuum leak, or drivability problems. The bolt is only preventing filtered fresh air into the PAIR valves themselves. Even if the bolt/plug were missing, "unfiltered" fresh air would be drawn in and pumped into the exhaust system, without any drivability issues. Personally, if it were my bike, I'd take them out. The carbs are out and everything is exposed. Why not?

I also see that you've removed the upper aluminum carburetor plenum/snorkel assy before removing the carbs (I've seen your other thread). Bad move. You'll never get it back together easily and it will fight you every inch of the way. It'll be virtually impossible to get everything back into alignment and assembled. After you've cleaned and rebuilt the carbs, be sure to re-assemble the entire carb bank before reinstalling (upper plenum/snorkel assy).

Carb Removal and Rebuild ( ST1100 ) *

Carb Removal and Rebuild ( ST1100 ) *

www.st-riders.net

PAIR Removal ( ST1100 ) *

PAIR Removal ( ST1100 ) *

www.st-riders.net

Hi afrymoyer,

I'm very happy that I joined this group. You have a sharp eye which helps me very good. When I removed the Air Chamber/Duct Assy and I had it off I knew: Bad move! Why? Because I saw that it will take a lot of time and swearing to get it assembled again. My bad. First time ever I removed the Carbs of an ST1100 and this is exactly why I joined a team like this. So, thank you very much as it helps me a lot on my next endeavor on ST's (because I'm starting to like them, hmm maybe because of my age...)

Thank you for explaining the PAIR system as that also helps me in decision to leave it or take it out. It's not my bike but I'll discuss this with the owner and as I like the chrome pipes I think I leave it where it is and unblock the tube. I read that the PAIR system is pushing fresh air into the exhaust for emission purposes and some say it can be identified it works if you hear plopping sound from the exhaust when decelerating. So I think I leave it where it is. It is harmless if the valves doesn't work anymore and it is harmless if the valves work correctly. So, I'm in favor of leave it as it is.

Thanks again for your help and sharp eye! I'll rebuild the carbs with a set of All Balls Carburetor Rebuild kit that can be obtained here in The Netherlands.

ST1100Y · 2024-11-13T03:37:51-0600

WillemVanKatwijk said:
...some say it can be identified it works if you hear plopping sound from the exhaust when decelerating.

Its actually more of a soft grumble while coasting....
Hard pops could be an indication of a vacuum leak...

I'll rebuild the carbs with a set of All Balls Carburetor Rebuild kit that can be obtained here in The Netherlands.

Based on experience (also/especially on 70ies & 80ies retro bikes) I would advise against aftermarket carb kits and prefer OEM...
Pattern kits stand out by sloppy finish, wide tolerances, sometimes won't fit or don't seal properly in the case bore, jets and gaskets/O-Rings included are just plain wrong for the model/version at hand, and the used alloys just love to corrode...
(on a 70ies SOHC the old but thoroughly cleaned OEM brass worked fine, attempts to use the Keyster kit only gave headache...)

Air Chamber/ Duct Assembly - Why is there a screw in this hose?

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