My lawn tractor (LT)will not start. When it is on choke it just acts like it is not getting fuel. When on run when I try to start it it backfires and will not start. I checked the fuel filter, chenaged the spark plug, made sure the carborator was not clogged cleaned out the carborator bowl. The plug is firing and the engine haws compression.

Why does the LT act likes it out of fuel when on choke but when I try to start it on run it backfires?