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The exhaust H-box is often removed due to the old one rusting out or being viewed as being unnecessary weight and complexity;
Do you need to rejet the carbs if you do remove it?
In general, no. You should not notice any difference - some say slight alteration in midrange power (power band moved slightly higher), some say no discernible change at all - if you remove the H-box and keep the stock carburetor jetting. That is assuming you don't make other changes at the same time, such as installing pod filters in place of the stock airbox - which definitely does require a carburetor rejet.
Not convinced about replacing your one that's full of holes? There's sometimes some on eBay US.
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