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        Exhaust sound changing on cold start 
        
 
         Hi there I have noticed my exhaust note changes on and off to a deeper tone on cold start up. it's not changing revs just sounds like it's getting deeper then stops. Some times it does it a few times on and off for the first minute of start up. I have a O2 controller and a fuel mod fitted is this normal? 
        
 
 Time spent without rod in hand is time forever wasted.
 
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          Time spent without rod in hand is time forever wasted. 
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