Have you thought about using a dB killer instead? These are little stubby pipes which fit into the exhaust (usually with a screw or bolt) and restrict the noise of the exhaust. They usually cost less than £20 for a pair and take minutes to fit.
The advantage is that you can easily fit them and take them off - saves you all the time spent swapping carbs and pipes.
You should be able to get them from most motorcycle dealers, or ebay. eg:
http://cgi.ebay.co.uk/ws/eBayISAPI.d...tem=8034240449