Small Engines (Lawn Mowers, etc.): Engine Will Not Start, spring retainer, fly wheel

Question
I have a Tecumseh 38701C mower. I was mowing the grass and the mower just died and I could not restart it. I checked the spark,OK. Bought some starting fluid to see if it was gas problem. It still would not start. While trying to start the engine, by chance put my hand on the exhaust and it sucked my fingers back against the exhaust. Now I think I have a broken exhaust valve spring. Am I on the right track? If so, what is the easist way to get to the valve spring/retainer to repair the problem? Any help on checking the valve spring or addition things to check would be greatly appreciated.  

Answer
did you by chance run into something or over load it in high grass , as to suddenly stall it out?  you may have sheared the key on flywheel  > thus off time?? .
and if thats not the case> to get to valve springs>  there should be on side of engine close to carb. mount to engine,  a sort of square plate, remove it and you will see the valve springs and push rods. while it is off, turn engine over by hand if possible, and watch them move. if there is a problem you will need to remove the cyclinder head and replace the spring, but you will need to remove spring keeper on valve and liftthe valve  up out of block. thus that is why head must be removed.
if fly wheel key was sheared> you will need to remove it to replace keyway. just by removing flywheel hold down nut and washer you can see at times if it is.