Another thing to check...
Check your headgasket,
If you pull the engine over with the pull starter and you hear a chirpping noise , it could mean the head gasket is blown or the head needs to be retorqued.... ( mose likely the three bolts around the exaust valve loosen over time.
Also, another way to check it is to squirt WD40 ( not a lot, just a little to mointen things up ).. in the cylinder around the head area, put the plug back in and try to pull start the motor.. the motor will smoke of course, so don't breath it in.. What you are checking for is bubbles around the head gasket where the wd-40 is squeezing out (Very small bubbles)
But listen for the chirp (do this without Wd40 in the motor) , as you pull it over with the plug in and the engine set to off....
Also, don't forget to get a valve cover gasket when you get the head gasket....
Good Luck,
Friiy