Small Engines (Lawn Mowers, etc.): rx75 stalls after 20 minutes of running, engine numbers, squeeling

Question
I have an rx 75 J.D. that runs well for about 20 minutes then shuts down.  Eventually it will restart, and it does start easy when it's ready.  I've run it until it shuts down then checked for spark and it does have spark so I don't believe it is the igniter or coil.  I don't believe it is a vacuum or fuel supply problem as I've checked the line and tank and both appear to be clear.  It's been suggested that it needs a valve or carb adjustment.  Does this sound reasonable?  It runs a Kawasaki 9hp however I can't get the flywheel cover off to get engine numbers for you.  I don't think I want to get "into" the engine and not so sure about tinkering with the carb.  I've jumped both the solenoid and starter and both seem O.K. although when turning it over when it is hot or for a slightly longer amount of time it does start shrieking/squeeling loudly(then stops while continueing to turn over) as I think the starter may be starting to go.  It does continue to turn over and the noise does stop but sounds horrible.  Are there any other things I should check before biting the bullet and taking it into the shop? This is actually a follow up as "John" is on vacation now.  Thank you for your time.

Answer
Mark:

I am not sure what john has told you, but if I was trouble shooting this, the first thing I would be doing is exactly what you did,  when the engine quits, check for spark.  Great Job!  

I am a little concerned with the squealing noises you describe and hope it is just a starter.  Be prepared however, these starters are very expensive.

The only test i can think of at this time is a fuel cap and remote fuel tank test.  So you can simply loosen the gas cap and see if the engine quits,  If so the problem is in the venting of the fuel tank.  Replace the fuel cap and you should be good to go.  You could also pull the fuel line off that leads from the fuel pump to the carb and see if you have fuel being pumped as well when you crank the starter.  Be CAREFUL though as a proper working fuel pump will shoot fuel out under pressure and quite far.  

If this still doesnt solve the problem, find a fuel tank off of an old mower (a lil push mower would work great) and attach it directly to the carburator and mount it higher then the carb so that the fuel flows by gravity.  If your engine doesnt quit you have isolated your problem to the fuel system venting or the fuel pump.

Let me know how this works for you.