I'm in a partially lazy mood right now so I let this webbie do the explanation with an extract:
http://www.moccsplace.com/images/pair/pair1.htmThe Pair Valve is a pollution control "Pulsed Air Injection" device, designed to "wash out" the purposely rich exhaust of the new metric bikes in order to pass EPA restrictions for import in the United States and other countries with similar restrictions. Many foreign designated models do not even come with a pair valve, although all other aspects of the bike's engine are the same. (The triangular (or oval) box is a tool box on most foreign models)
The sole purpose for the Pair Valve is to passively "Inject" fresh air into the exhaust system at the exhaust port, to cause ignition of unburned fuel vapor *before* it leaves the exhaust pipes, or to thin out the mixture with enough air to fool the sniffer machines. Unburned fuel vapors enter the exhaust system whenever you back off the throttle, or gear down. When you close the throttle, as in gearing down or slowing down, the drop in vacuum at the intake port allows the Pair Valve to relax and open and allow air from the air filter box to be "siphoned" into the exhaust port by the negative pressure at the exhaust ports. (there are reed valves in the pair valve to prevent backflow from the exhaust to enter the pair valve and airbox during roll-on and subsequent positive exhaust port pressure)....
For the uninitiated, PAIR system simply injects a bit of fresh air from the airbox into either the header (for older model EFI bikes) or into the cylinder heads (for certain newer models) to simply to lower the CO content of the exhaust gas to pass emissions requirements. This is pretty important in certain states in US (California have pretty high emission standards compared to other states) and most European countries.
Fortunately, Singapore do not have this high of a standard.... yet. Being a Italian model, the Ghost naturally has the PAIR system installed (thanks to a local fellow Gisser for pointing it out despite my objections).
Now, what's the point of removing it, you ask?
Simple.
For stock exhaust systems, no point. Or rather, not that much of justification to spend 1-2 hours of an nice warm Sunday afternoon sweating it out and getting more cuts on your hands and palms doing the PAIR system removal.
But for those with aftermarket exhaust system, the annoyance is pretty apparent when you go near WOT at 1st or 2nd gear and close the throttle immediately to slow down.
You suddenly have a flatulent donkey for a bike.
Where did that come from?
Well, I won't explain the physics much because the link I posted very much explained everything.
Instead, I'll get down on what needs to be done.
The PAIR valve consists simply of a solenoid valve with 3 I/O ports (1 input and 2 output), a reed valve buried somewhere inside the top head of the engine and 3 hoses. The solenoid valve is controlled by the ECU to when it should open and let the air into the cylinder head and when it should closed. The reed valves simply prevents exhaust feedback into the airbox. 1 hose goes from the airbox into the solenoid valve and 2 from the solenoid valve into the cylinder head to the reed valves.
Simple, capiche?
A friend from the UK GSR forums (thanks Bazz!) dropped a line to me on the steps. Essentially, there's the easy way and the hard way.
The hard way involves fabricating some sort of steel plates to block off the reed valves and thus eliminating the need for the reed valves as well as blanking off the output at the airbox, etc, etc.
Being a shortcut bastage that I am, I go for the easy. It'll costs about SGD$1 and about 1 hour if you have the tools right.
What you need:
3 x M14 bolts of 25mm length. No longer coz that's all the length you have to play with.
Heat-resistant silicone. I didn't have any and it'll take 24 hours to dry properly lest bits are sucked into the cylinder head. So I use the next best thing: plumber's white tape.
Tools to lift up the tank.
A small plier (not cutters, mind you).
Lots of bandages.
Steps:
Lift up the tank and prop it.
Take off the airbox. I'll give a little tip I learnt: you don't have to take off the cover and the filter as the tech manual suggested. Just unscrew the 4 screws clamping the airbox to the throttle bodies, unhook the 2 air hoses (clue : one of them leads to the PAIR solenoid valve), the IAT sensor plug underneath the airbox and the IAP sensor attached to the back of the air box. Done. you can lift it off.
Look at the space just above the radiator on the inside of the chassis. There's a little black plastic thingy with 3 hoses going into it.
Can't figure it out?
Using a plier, unhook the clips and pull out the hoses. Leave the solenoid valve where it is and hooked up to the ECU. This is important and I'll explain it later.
Now, take the 3 M14 bolts. Before you begin... erm.. screwing around, take the silicone and start applying it on the thread. Me, I use plumber tape. The idea is to seal up any possibilities of the thread letting in air once its screwed into the hose.
Now, start screwing. The bolts into the hoses end, of course. Take care for the hose that leads to the airbox. Make sure you screw the right end in (the one with the thicker hose clamp).
Once you've screwed the bolt in the best you can, use the pliers and slide up the hose clamp to secure the hose tightly against the bolt. If you have some spare cable-ties of suitable length, go ahead and have fun also.
Once that is done, you're done. Put the hoses back into the front space of the chassis. I took some spare cable ties and looped both hoses to the solenoid valve to keep it from moving around too much.
Next, put back the airbox and the rest of the tank back on.
You're done!
Why leave the solenoid valve hooked up to the ECU?
Simple. The solenoid valve is acting as one of the active sensors for the ECU. Removing it and you'll get an annoying FI warning light up.
Bazz told me a 20ohm resistor will do the trick. He's working on that and will update me.
Ditto for me to here.
I've tested it on my carpark and it seemed to work well. By my rough guesstimation, at least 70% of the backfires on a closed throttle from WOT at first gear is gone. Some still exist but right now, my PC3 is off and I'm back on O2 sensor until I get the time to have Racewerks fix it back on.
Later tonight, I'm riding to a friend's place a distance away and I'll be able to fully test it.
Do stay tuned....
