Clogged up main jet in the carb. If it dies when you push the choke in, then it's not getting enough gas. Replacing spark plug(s) on a 4 stroke to solve a problem is not right. I've run the same plugs upwards of 4-5 years, and when things are tuned right, they remain light brown, no carbon, no oil fouling. Take the carb apart, and clean the internals with car cleaner, don't waste time and energy trying to spray it from the outside. Good luck