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the pair system is a controlled exhaust leak that by design causes popping by at certain times letting filtered fresh air into the exhaust so that the extra o2 can allow some of the incompletely burned gasses to finish burning. You hear this combustion as pops during decel but is usually not very noticeable with the quiet stock muffler. Usually pops that become more noticeable with a louder aftermarket pipe can be greatly reduced by blocking the pair hose(s) but this may cause more emissions and cause acid rain, melting of the north pole, dead whales, depletion of the Brazilian rain forest, and a decrease in Al Gore's bank account.

It could be considered tampering with the emission control system so I have never blocked it, nobody saw me do it, you can't prove anything.
 

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I can see what youre saying about it throwing off the AFR readings, but Im curious how it stops the popping and why its recommended to remove it when installing an aftermarket exhaust/fuel controller if there are no performance gains. Not trying to be argumentative or anything like that. I am genuinely curious, is all.

Thanks for the great info on this subject! Maybe we could take the posts about the PAIR valve out of this thread to keep it on subject and create a stickied thread for discussing the PAIR system?

Admins? Yay/Nay?
This will take a little while and corrections, disagreements, or criticisms will be welcomed.

The catalytic converter on motorcycles are generally a hard porous cylindrical devise that the exhaust heats up as it goes thru. The unburnt gas in the exhaust is wicked up in the cat and the heat in the cat creates a sizzling burn off rather than an explosion.

The pair valve injects fresh air into the exhaust to bring the rich unburnt gas closer to the 15 to 1 combustion ratio so it ignites easier when it goes into the cat. They do work quite well and with very little backfiring.

To block off the pair valve with the stock muffler still on makes no sense to me.
Nothing is gained.

To not block the pair valve and run an aftermarket muffler with no cat just introduces unburnt exhaust into the muffler that is ready to ignite and backfire.

To block the pair valve and run an aftermarket muffler will minimize the chance of backfiring because the unburnt gas will still be to rich to ignite and just pass thru.

It is more of a situation of not, that blocking the pair valve prevents popping and backfires, as that by leaving it active it creates the perfect possibility for popping and backfires to happen.

The only real world benefit of disabling the pair valve with an after market muffler is that the muffler wouldn't have to be repacked as often.

All in all it's not really that big of a deal. Sometimes a burble, a pop, and a backfire is fun to hear.
 

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I will attest to the benefits of blocking the pair valve on a bike with adjusted air-fuel:

With the pair valve hose blocked (using a foam ear plug), O2 sensor disconnected, air box cover removed and with a pc v, high flow air filter and non stock muffler (with baffle in) installed my 250 runs as smooth, if not smoother than stock -- no backfiring at all, engine warning light remains off and sounds quiet too.
 

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I will attest to the benefits of blocking the pair valve on a bike with adjusted air-fuel:

With the pair valve hose blocked (using a foam ear plug), O2 sensor disconnected, air box cover removed and with a pc v, high flow air filter and non stock muffler (with baffle in) installed my 250 runs as smooth, if not smoother than stock -- no backfiring at all, engine warning light remains off and sounds quiet too.
Mine runs fine with slip on and pair valve blocked. Didn't d/c my o2 sensor as I didn't believe I had to due to not having a power commander. It reduced the backfiring just blocking the valve.

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the pair system is a controlled exhaust leak that by design causes popping by at certain times letting filtered fresh air into the exhaust so that the extra o2 can allow some of the incompletely burned gasses to finish burning. You hear this combustion as pops during decel but is usually not very noticeable with the quiet stock muffler. Usually pops that become more noticeable with a louder aftermarket pipe can be greatly reduced by blocking the pair hose(s) but this may cause more emissions and cause acid rain, melting of the north pole, dead whales, depletion of the Brazilian rain forest, and a decrease in Al Gore's bank account.

It could be considered tampering with the emission control system so I have never blocked it, nobody saw me do it, you can't prove anything.
Not that I'm planning on tampering with the emission system :) but when pair valve is blocked adjusting the idle on our bike becomes a reality right just by turning the idle screw (the one that has white paint and is written by Honda as "do not adjust") since the ECU now no longer is adjusting things because of the pair valve , true?? or am I off by a mile!
Richard
 

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Not that I'm planning on tampering with the emission system :) but when pair valve is blocked adjusting the idle on our bike becomes a reality right just by turning the idle screw (the one that has white paint and is written by Honda as "do not adjust") since the ECU now no longer is adjusting things because of the pair valve , true?? or am I off by a mile!
Richard
not true. You might be thinking of the idle air control valve which is completely different..

and if you mess with that you'll screw something up for sure.
 

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OMFG. I had the 5k rpm engine rattle. I checked out my pegs and sure enough the washers on both sides were loose and not flush!! I tightened those bad boys and voila, rattle gone! Thank you sir! You have saved me a tremendous headache @HeadshotLocke.
 

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I have tried checking all the bolts and nuts and there sound is not coming from the cover sets...or any other parts outside from the bike ....i think it most probably caused by the valves......any one tried..
 

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