some simple things that can you can do to try to stop it...
what plug are you using? upgrading to an NGK will help. i run a B7HS, and have used the B6HS as well. the 7 is a colder heat range, and it works for me in California, but my motor's got some performance tweaks.
get a new plug wire, too, if you haven't already. i use a copper core 7mm wire.
something as simple as a weak spark can make it sputter at full throttle.
match the intake manifold as much as you can, you can't get it perfect, because there's not enough metal, but you can open it up. also, grind away the casting flash on the inside of it. you don't want a mirror finish, because the fuel needs turbulence to atomize properly, but getting rid of "obstacles" like the bad casting marks helps.
what's your needle setting at? mine's second notch down. playing with that will affect fuel flow, just keep an eye on your plug color so it's not too lean, or too rich.
fuel mixture has an affect on it too.
and make sure your air fliter's clean. it'll clog up with oil and won't breathe.
de-carbonizing the top of your piston helps, too. just pull the head, put the piston at Top Dead Center (TDC) and spray it with some carb cleaner. i use a toothbrush and scrub it a bit. some stuck chunks can be scraped off with a knife, or a scotchbrite pad.
DO NOT use sandpaper, steel wool, or any other abrasive that can get into the cylinder, and make sure the chunks you clean off don't get in there, either.
scratched cylinder walls will be waaay worse than a little four stroking...
one last thing, did it sputter when you had the baffle on?
my motor is running with no gap on my plug idk how but it is. iv been looking at a spark plug on spooky tooth cycles it has 3 prongs on it instead of just one, what do you think???
