need some help it sounds great up to quarter throttle then spits sputters and backfires,cleaned carbs new plugs drained muffler still the same any answers would be great

thanks rodman

 

Did U say "drain muffler"? Did it have a bunch of water in it? If so, could there still be a bunch of water in the pipes closer to the cylinder? The other things that I would check is the valve clearances (it almost sounds like they arent closing/ or are out of time) the other thing that I would check is your air/fuel mixture. Try putting on/ taking off the choke and see if that helps. Try it with your air filter off / air box open. I would start with the air/fuel stuff first. hopefully you can quickly track down your problem. also, take off your fuel line from the carb and make sure you have a good flow of gas coming out of it.
Good luck
esonnen