Probably the usual sportster syndrome
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Fitted drag pipes and it wont run right. 883 loses about 6~8 HP with drags and carb set up is a nightmare (you can make it run at 7,000 rpm but cam is only good for 6,000
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) Best thing to do is fit a 1200 kit, its worth about 20HP then work from there (done a lot of them to 883, just over 0.500" overbore)
Need to find out what BS mods were done first
PJ