Small Engines (Lawn Mowers, etc.): Wrong oil in an Eager-1 - how bad?, craftsman eager 1, mobil 1 synthetic oil

Question
I just picked up a used Craftsman Eager-1 22" mower with a 5.5HP engine.  It hadn't been used for about 3 years, but when I filled the gas tank she started right up and mowed my lawn just fine.  After I was done (I know, I'm an idiot), I decided to check the oil, and low-and-behold, it was empty.  Then to compound the problem I went and added the same Mobil-1 synthetic oil (15W50) that I use in my car.  Now it starts ok, but doesn't run well.  It dies if I run it at full throttle and hesitates and sputters at mid throttle.

Did I do a bad bad thing, and if so, can how can I fix it?  I assumed (probably incorrectly) that since Mobil-1 is supposed to be a really good oil, it would be good enough for the mower....

Ian

Answer
Ian

Remove the oil you put in and install a straight 30w oil,the mower will run better. The oil you used is way too heavy for the small engine.As far as damage it may have gotten too hot and warped the head. You may want to check your breather and the carb looking for a oil buildup. Pull the spark plug and check to see if it is fouled. I would replace the spark plug just to make sure some plugs foul and wont work correctly.