Small Engines (Lawn Mowers, etc.): hard start/short run problems, throttle shaft, air leak

Question
I have a Toro GTS SuperPro Recycler 5/600 lawnmower Model#20439, Serial#3902912. After working it pretty hard a couple of weeks ago, I let it sit until yesterday then it stalled after using 20 minutes and wouldn't start.(I should note that it was very hard to start before I used it yesterday, and before stalling). I tried starting it again this morning and nothing. Took the spark plug out and not knowing what the correct gap should be, it looked o.k. I did not check for spark at the plug electrode, but I took the plug wire off the plug, and checked for spark there by holding wire 1/4" from engine block (saw a faint spark), but I was working on it in sunlight.  The spark appeared yellow.  I thought a good hot spark would be blue-white.
Took the air cleaner assembly off including the 'base' from the carburetor so I could better see the choke plate and throttle mechanism. I disconnected the fuel line to the carb...plenty of gas there, so no fuel restriction.  I had an inline filter installed a year ago.  So, after putting it back together, I finally got it started...but only for a couple of seconds.  I played a little bit with the fuel mix valve, and not much of a change.  It finally ran for about 10 seconds, and as I was watching the Control Throttle shaft and the Choke Shaft, it seems to me the throttle shaft moved
first, then the choke, then it died. I am thinking they both operate off a vacuum.  Maybe I'm getting an air leak, or perhaps it needs an armature-magneto. It is acting like it wants to start.  It fires up after 1 or 2 pulls on the cord
every time...just keeps quitting.  Any help would be appreciated. The neighbors are starting to give me dirty looks when they drive by, and I don't want to buy a new one.  Guess I will if I have to, but don't want to.
Many thanks,
Alton C.  

Answer
Here is the service manual form the GTS 150.

1 go to www.toro.com
2  click on look up parts for homeowner
3 enter your model  number in the appropriate box
4 do not enter your serial number the one you gave was invalid
5 click on the 39000000 serial range
6 click on manuals
7 scroll to service manual for GTS150 link
8 click on link

Your service manual for the entire engine will download for free.  Check out the fuel system, electrical system and BBC control system.  This should help.