2000 25 4stroke loss of power in midrange

[skiffman]

What we have here is a engine that idles fine and will run fine at the top range. It however for a short spot in the midrange will loose power and at times backfire. It does not die. I have replaced the filters, fuel line, plugs,thermostat. Any thoughts would be welcome!.

[boats.net]

Check belt timing. May need carbs cleaned.