Had this mower about 10 years and was going strong untill I tried to run some old old filtered fuel thru it. Big mistake. Long story short, I wound up removing the carburetor and cleaning it as well as flushing out the fuel tank, new spark plug, replaced the fuel line. Now when I try and pull start it, it's like it has no compression at all and wont start. Almost like there is a compression release that is stuck open or as if the spark plug is removed?? Really weird. Does anyone know if this self propelled model has a compression release? If not then It may be a blown head gasket but I don't see how, it just sputtered and sputtered with the old fuel till it wouldn't run at all. Appreciate any help or advise.