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Thursday, October 7, 2010

PAIR Removal

Most new Hondas (and other new motorcycles) are equipped with a PAIR or secondary air system. PAIR stands for Pulsed Air injection. It is sometimes also referred to as a smog pump. The purpose of this device is to burn off unburned hydrocarbons in the exhaust in order to meet emissions requirements. They typically only operate during high-vaccuum conditions and work by drawing filtered air from the airbox and pulsing it into the exhaust port. On closed-throttle decelleration the PAIR system can usually be heard popping... it sounds like a backfire. Here's a basic diagram from the repair manual:

I like to remove this equipment for a few reasons:

1. I don't think it's neccessary. I'd be willing to debate its pollution-fighting merits if anyone cares but I'll spare you the rant for now

2. Removing the system eliminates a lot of clutter in the engine bay, making maintenance easier.

3. Dyno tuning becomes simpler, as the system confuses the tuner's "sniffer" that measures the air/fuel ratio.

4. It's fun to take apart motorcycles and put them back together. :) Especially Hondas.

Here's how it went. First I lift the tank and support it with a strap:

Next I take off the airbox cover.

This is all the crap (bugs mainly) that came out of the air filter when I banged it on the floor:

Top view of the inside of the airbox. The layout of the throttles repeats the offest layout of the cylinders with their growly firing order.

There is a little hole in the side of the airbox where the PAIR draws air in.
From the outside: this is the suction line that feeds the PAIR
Bottom of the airbox and ECU removed:
The 2 silver pods with hoses attached are the PAIR valves for the rear cylinders
To get to the front cylinders I had to remove this engine shield that sits over top of the cam cover. The manual says to remove the throttle bodies to get this out but I didn't want to go that far. A bit of wrangling and some skinned knuckles and I popped it out:
Here are the front PAIR ports, housed in one double-sized pod: (look next to the hose and hose clamp)
Rear cylinder head with PAIR valves removed and the holes left behind:
The holes need to be covered up, as they drop right down into the combustion chamber. A "block off kit" is needed. There won't be much of a demand for kits for the VFR (typically this mod is only performed on race bikes or heavily tuned bikes) but I studied some parts diagrams and found that all recent Honda sportbikes use 1 of 2 different valve assemblies. Multi cylinder heads (CBRs) use a pair of twin-port units while single cylinder heads (RC51) use a single valve unit. I contacted Kyle Racing and ordered a CBR kit and a RC51 unit.  Here are the plates, machined out of aluminum and anodized in black:
I spread on a very thin layer of gasket maker and slapped them in place. I was careful not to over-torque (and thereby ruin a cam cover)

Here are the rear block-offs bolted in place. On the right of the image you can see the motor that controls the throttles.
The double-sized front block-off bolted in place:
This is what was removed: 4 pair valves and their associated hoses as well as the control unit.  Unlike the purely pneumatic system on my CRF250x, this one is run off a solenoid. I was initially concerned that its absence could throw a fault code, but after studying the trouble code guide and wiring diagram, I don't think it gives feedback to the fuel injection system so it shouldn't be an issue. If it does trigger a fault code, I can remedy it by shorting the wire with a 25 ohm resistor which will "simulate" the presence of the solenoid.

The intake port had to be plugged, otherwise it leaves a hole into the airbox where debris can be sucked in. Typically a hose cap is used. I used a windshield screw. (the type with the expanding rubber  nut and washer)
Then I just had to put it all back together. I was careful to lay the wiring harness correctly as Honda intended. It only fits one way, and it fits perfectly.  I also made sure to clean all of the internal airbox and throttle parts so dust won't be sucked in.

This mod doesn't increase performance, but it gets rid of a lot of bulky unneccessary junk and it gave me a good excuse to dig into the guts of the bike and learn how it all goes together.


  1. If you keep like this your bike will be a lot lighter.... ;)
    stay cool, great blog!

  2. Wonderful! I'm always for making maintenance simpler.

  3. Thank you for great photos and explanation.

  4. Awesome write up! I'm installing a Dynojet Autotune next week and this is exactly what I needed to know - since the instructions state the PAIR must be blocked or disabled. BTW did you ever get a fault code for disconnecting the solenoid plug? Thanks!

  5. Did you keep the two white plastic containers in the airbox? Are they for better resonance or just to suppress intake noise?

  6. anon: nope, no fault code. The solenoid doesn't give feedback to the ECU. It's a 1-way system.

    alang: I haven't touched them. I'm wondering how much different it would sound if I yanked them out? If they're anything like the resonators on car intake tubes they're there to suppress intake "whoosh". Why don't you pop them out and report back? They're riveted in... you will have to break them off.

  7. Here's a question for you - I bought the Dynojet Autotune part# AT200 which is the single channel unit. The instructions state to install the O2 sensor before the cat in the collector. Looking at the OEM 02 sensors there are one each for each bank before the cat. I was wondering if I needed AT300 dual channel O2 sensors to ensure an accurate reading for both banks (front/rear cylinders). What are your thoughts on this? The Dynojet website references the AT200 (single channel) AutoTuner for the VFR1200F. Any feedback is greatly appreciated.

  8. I'm a little afraid to answer because I'd only be guessing. But if it were me I might splice them to only take the single reading from your power commander. I'm not sure the PC5 autotune is capable of multi-bank or even multi-cylinder closed loop feedback. The VFR1200's odd firing order might screw up the dual channel sensor. All it's doing is taking the place of the a/f sniffer a dyno tuner uses to override your bike's fuel injection.

    Better talk to Dynojet on this one.

  9. I had similar interest in doing this with a CBR1100XX a few years ago, but I was concerned about the extra stuff or the associated weight. I just didn't like the idea of air in the airbox bypassing the engine, thereby lowering air pressure in the box. So I simply loosed the hose at the airbox and stuffed it with polyurethane foam, then covered over the end of the hose with a piece of nylon bug screening stuff, and put the hose back in. I didn't know exactly how much restriction this added, so it was very much a seat-of-the pants thing, but it seems to me that the bike did run just a little bit smoother after than, which would be attributable to steadier pressure in the box. That was what I wanted to accomplish, and I prefer to keep the bike stock as much as possible. In the past I've ended up with small boxes full of parts that I taken off a bike or a car, and when the time comes to sell it, there is the hassle of either tossing it all out or trying to put it all back on.

  10. The last few times I've sold a motorcycle I've taken the time to put it back to stock and part out all the aftermarket goodies. The weekend's worth of work is usually worth a couple grand. I'll probably never sell the VFR1200 though.

  11. Did this change the exhaust sound any? I have BOS exhaust and the bike has been run in Dyno so it should not run lean. I still have some "backfire" noise when i twist the throttle (the bike is not moving). Could this be PAR?


  12. Could PAR somehow be desabled without removing all the parts? It would be nice to test the affect first. If there is no big affect it would save a lot of work.


  13. Yes. All you would need to do is block the hose which feeds the PAIR valves. It's located on the right side of the airbox.

  14. Remove enough stuff and we can through in a bigger fuel tank...

  15. Do you still have the PAIR valve itself? When unplugged, is the valve normally open (lets air be sucked into the combustion chamber) or normally closed (blocks air box from the rest of the system)? I'm wondering if it would be as easy as just unplugging the PAIR valve. Ideally, I would just install the PAIR block-off plates as you did, but realistically, I'm sure I wont be able to get to the front cylinders without breaking something.

  16. The PAIR valves can be disabled simply by blocking the hose that feeds air from the bottom of the airbox. No need for removal. I chose to remove because I wanted to get rid of the weight and clutter.

    1. I completely understand why you went through the process of installing the plates vs just blocking the intake hose. If I was confident enough in my abilities (or you lived any closer), I would install the plates as well.
      The plates are the better way to go, no doubt. I was just thinking what would happen if I just unplugged the PAIR valve from the ECU... would I get the same effect.
      My concern is that I don't know how much vacuum is on that intake line. I know I could plug the intake hose with marbles, but if I just plugged the hole in the air box, I'd hate to have the plug sucked into my system and cause me all kind of headaches. Unplugging the valve seems like the 'easiest' way to go... assuming that when unplugged the valve stops air flow.
      I'd like to disable the PAIR system so everything is ready if/when I get a PCV and I'd like to stop the popping on deceleration.

  17. Done the mod today, I had to since I will be installing autotune next week. Few things came up as I did thins, that plastic piece under ECU was a **** to get out, and than put back in. I ended up breaking a piece of it but it went back in more or less, if I have to I can always lock it in place with some expandable foam or something like that. And I didn't realize the hole after removing the hose would be such a pain to plug, I got red RTD from ORaily and asked about a windshield screw but they didn't have any [or knew what they were] so I taped the hole over and silicon-ed it shut. I'm a little worried now, will there be enough vacuum on it to rip that patch off and suck it in to the intake? I'm thinking about getting a piece of rubber and some hardware from home depot and making my own expandable plug, half an hour of searching on the web yielded no useful results. Anyway, overall great DYI guide, hopefully with this and autotune my VFR will get smoother at low RPM's.

  18. Hi there.

    You have a very good write up here and very good photos.

    I am Nick Iliopoulos from SmartMoto. We have created a complete PAIR valve removal kit for the VFR1200F and the Crosstourer 1200 and we have it listed here: http://www.ebay.co.uk/itm/261743126358

    I am writing to ask you if we can use your photos to our installation instructions because we develop all our PAIR valve removal kits directly to the valve covers of the engine and not to running motorcycles. We would mention you in our instructions.

    1. Thanks for visiting Nick and thanks for offering this kit to VFR1200 owners. You have my permission to use my images, thank you for asking. I would appreciate if you included a link to my blog in the instructions and if you have extra parts I could really use a proper hose cap and clamp for the air inlet.

    2. Hi again.

      I just added your link to our installation instructions. Yes I can send you a hose cap for the airbox. You can find my ebay shop at: stores.ebay.co.uk/smartmoto please send me a message there and we will send you the cap.

      Thanks again

  19. Excellent instructions, my dear sir. 20 minutes ago, never had I heard about PAIR existence, even less about why one ought to remove it, but now I'm done reading your post, I cannot anymore ride my VFR with that crap still on it. That thingy must leave!