That's exactly what was happening to mine. I had a straight pipe on mine but ended up going back to the stock muffler. Just can't wait to get it back from paint.

 

CBRew900rr: i have a quick question for you, do you clean your own carbs? and if you do! on your bike where the vacuum line comes off of the bottom of carb number 3. does that vacuum line go straight to the gas tank or is it into a tline that splits one to the tank and another one to another carburetor vacuum port.. do you know what i mean??