Sounds like a caburation issue to me. A throaty sound most likely means itss not getting enough fuel in the mixture once you open the throttle. You can test this theory out by closing the choke a little as you open the throttle to see if the power increases. This should suck more gas into the mixture and increase the combustion & rpms. If that turns out to be the problem you might try first running a bottle of Techron fuel system treatment through to clean things out before you start foolng with the jets and dismantling the carburator to clean mechanically.