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By
Bayouboy 03/2004 Here is a short and sweet description of what I
believe to be correct but if I get something wrong I'm sure a more
knowledgeable member will put us straight.
The PAIR system is for
pollution control. It consists of a solenoid valve which can allow
air to be directed from the air box into the exhaust path. When the
ECU (bike's computer brain) thinks there may be a good chance that
some unburned gasoline is being released into the exhaust pipe the
valve opens and lets some air into there too. The ECU will use input
form various sensors (engine rpm, throttle position, O2 sensor if
present, etc) to decide when this might be happening. The hope is
that the oxygen in this air will react with the unburned gas to form
carbon dioxide and water thereby preventing the release of unburned
hydrocarbons, hence reducing pollution.
One of the side effects of this system is that when you 86 the
restrictive stock exhaust and put on a free flowing aftermarket pipe
you will hear backfiring as the air pulse from the pair system hits
the unburned fuel in the pipe and detonates it. This will primarily
occur when you roll off the throttle. Of course since this
detonation is not occurring in the cylinder it does nothing for your
bike performance except give it cleaner emissions.
If the backfiring sound bothers you, you can defeat the PAIR system
and stop it form occurring. There are a couple different approaches
here depending on what exactly you would like to accomplish. If you
decide to defeat the system you may want to go the full nine yards
and remove all the associated hardware like the solenoid valves and
tubing, etc. This will allow you to shave off about 4 pounds of
weight. Its kind of complicated to do this and you will need to get
metal plates that can be mounted to the cylinders to plug the holes
formed when removing the various bits. Also some monkeying around
with wiring is required so no warning lights come on and everything
works properly. However this is doable and other members have done
it. You can find out how with careful searches of this forum.
I did what is referred to as the poor man's PAIR Mod. I simply
plugged the hole that the PAIR system gets its air from and that
made the backfiring go away. Now I have 4 pounds of useless hardware
stuck to my engine. The ECU still tells the valves when to open and
close and they still open and close when told to. But nothing passes
through the valves cuz I screwed a 3/8 in bolt into the air intake
(see pic). Others have plugged the hose that is connected to this
intake with a ball bearing essentially accomplishing the same thing.
It would be nice to get rid of the 4 pounds but I want to be able to
easily return the system to stock for service, or inspections etc.
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