Monday, 22 July 2013


APRILIA RS 125 Exhaust Derestriction

The later bikes 2003 onwards have a CAT in the expansion chamber. In the expansion chamber not the end can. To get rid of this CAT which makes your bike perform differently, get an after market expansion chamber (best buying the end can with it) or buy an earlier expansion chamber from an RS125 or take the expansion chamber off and be prepared to cut it open, remove the CAT and weld it back together.

If you are going to buy a different expansion chamber then you will have to rejet your carb. The bikes with a CAT in them are set to run rich (more oil) because the CAT requires the bike to run like this. Therefore you will need to buy a standard main jet for your carb. If you have a 28mm carb then your standard main jet size is a 120. If your carb is a 34mm your main jet is more likely to be a 158 You can get these quite cheap. This means taking your carb off and removing the old main jet, and replacing it with a new one.

The racers tend to use the standard expansion chamber because it is thicker then aftermarket ones therefore contains the heat more, and these work better with more heat. They normally just change the end can.

The expansion chamber doesn't really have anything in it anyway if your thinking this was too simple. Literally just cut it open, remove the CAT and weld it back together.

Aprilia rs125

Some exhausts also have a recirculation tube that goes to the air box. You just have to cut this off and weld it up and seal up the air box.

The snorkel in the air box can be taken out too, this will let some more air in slightly and make your bike sound a lot better. Just pull the rubber out the top, or you can cut the part that sticks out. This shouldn't affect your jetting since the bike is not jetted correctly from standard anyways. If you want to be sure stick a bigger main jet in (121 on a 28mm carb). Do a plug chop to confirm.

you could just buy yourself a sports exhaust , cost more but less weight .

see the full derestriction process here 

see more Aprilia RS 125 posts here 

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