I have a Craftsman 18in chain saw + when it has been running awhile it starts to bog down. If it cools off it will run. I changed gas lines + plug. What to do next

 

Make sure your chain oiler is working and the chain tension isn't too tight. A chain that's binding will bog the engine down.

If that's OK, if the engine quits altogether, check for spark - the coil could be acting up.

If it doesn't give out altogether, go to your hi/lo screws on the side of the carburetor and turn out the hi speed about 1/16th of an inch. That will richen up the mixture - it may be running hot.

Also check the gas cap vent to make sure it's clear.