help please????
 

Me and a buddy of mine just put in a 2009 mercruiser 496 mag,375 hp into our boats,his is a `97 mine is a `01,both the same modles,bayliner ciera comand 2858.Both have bravo 3`s.The problem is my fuel consumption.He burns 56-60 litres an hr,while i`m burning 80-88 litres/hr.This is at the same speed,28m/hr, side by side,fuel from the same pump,motor installed by the same mechanic in the same month,same motors. He`s reving at 4400 rpm i`m at 4300 rpm.The boats weigh in with 350 pound difference,i`ve even stripped all my gear off and still sucked back 79 L/hr. I also have a backfire when getting on plane or when running full out(i`ve only done this once).I had the mechanic hook up his computer/scope? to the engine while running at various speeds and there were no faults even when back firing.Something is wrong but he can`t figure it out.Does anyone have experience with this problem or any guesses? I`d appreciate any help i can get.

how do you know fuel consumption?you have a flow meter on your fuel line? Same props? same trim position? tabs?I know you stated you stripped some wieght out but have you actually wieghed both boats?