You can add a fuel additive to your gas or just use Poulan 40:1 it has the additive already in it. You also might need to clean the gas filter.
Very important that the oil to gas ratio is exact. Also use fresh gas and keep the oil clean, filled and clean the air filter with soapy water.
Can also spray a squirt of car engine carb starter after taking off the air filter or a tap. of gas, then start it, let t run for 5 minutes, shut it off and replace the filter.
Spark plug may appear OK, but won't hurt to replace it.
This is the experience I had with a different trimmer.