I have a Poulan pro chainsaw. It has started having problems. What is happening - It has three settings - full choke (that part works) then you switch to middle - the chainsaw starts, and runs. But as soon as I hit the trigger which turns off the choke - it stalls. However If I pull trigger, and keep running engine it will stay on and I can cut wood - but as soon as I release trigger to idle - it stalls. In other words it will not idle w/o stalling, and I also noticed it doesn't have the power it had before this problem. Any suggestions on what to do. I have not replaced Spark Plug, or filter - but I would think it would be another problem... carb? Thanks.