i have a 2008 Volvo penta 3.0L that is backfiring through the carb, and will stall if given any gas to reach plane. ill have to work the throttle to get it to get up on plane. once it is on plane, you can hear the carb backfiring and coughing while on throttle. the engine will fire right up and idle just fine, but when throttle is pushed it starts backfiring and getting ready to stall. the engine has 62hrs on it. I bought it used and am about to start trouble shooting it but I would like to know where to start. thank you for reading