First you need to find out what jets are in the carbs. If they are stock, you may have a vacuum leak or a low float level. Also check the pilot air screws. They do make a difference above idle. Unfortunately I have never worked on Rebel 450 carbs, but I am assuming they are pretty much the same as any other CV carb.
2016 Rebel, 2013 Royal Enfield B5, 2009 Genuine Stella, 2006 H-D Sportster 1200, 2006 Vespa GT200, 2001 Yamaha XT225
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