I've had a McCulloch MS1839 chainsaw for years. Recently the chainsaw has become difficult to start. I take out the spark plug, clean it off and it starts easily and runs as long as I hold the trigger slightly. At idle, it stalls after 15-30 seconds. Then I wipe the plug and go through it again.

The problem seems to the spark plug getting wet from the gas / oil mixture.

Suggestions, please.

 

Most of those carbs have a L and a H screw for High rpms and low rpms. You might try turning the L screw in a little at a time until it clears up, if it does. Also check the choke to make sure it's coming off.

As the carbs age they can develop leaks and need to be rebuilt or replaced.