If your trying to clean out your exhaust chambers (the big metal bulbous things), then you can do a couple things. After market chambers that are simple all hollow inside can be cleaned out with a wire brush attached to a drill. Of course the wire brush needs a good long reach, and I have yet to see one that you can buy from the store.
So with that said, you can always make your own.
Go to your local hardware store and get a good long section of plastic coated cable. Get a good thick one, but not so thick you cant get one end in the chuck of your drill.
Cut the plastic coating away for about 5-6 inches on one end. Unravel/wind the strands of wire in the cable and fan the all out.
Take a piece of PVC tubing (just needs to be big enough to get the good end of the cable in, push the PVC pipe so it slides over the unwound wires so you can slide it all into the end of the exhaust. Attach the good end of the cable to the drill, slide the PVC tube with the unwound wire end into the exhaust chamber, pull back the PVC pipe towards the drill and use that as a handle. Let the drill ripe and the wire brush will break up all the carbon build up.
Do this to both ends and you should be good to go.
Of course with stock exhaust chambers there are metal baffles and walls and crap all inside there, so this won't be the best solution. With that, your best bet is to drop some money on some new after market chambers
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Charles Gallant