Small Engines (Lawn Mowers, etc.): Lawn mower troubles, small engine mechanic, briggs and stratton

Question
I have a Briggs and Stratton walk-behind mower that is approximately 4 years old.  ( 3.75 HP, Model #98902, Type 1100E1, Code 98111151) It has been sounding rough for about the last 3 weeks and now is to the point that it can be started, but then immediately fails. I changed the oil, drained gas and replaced with new gas, changed the spark plug, cleaned the air filter.  I am no mechanical genius but did make an attempt to look in the carburetor.  I removed the air filter and loosened the screws attaching the carburetor to the gas tank.  There was a small spring (maybe 7mm X 20mm) sitting sideways between the carburetor and the gasket that lies on top of the gas tank.  I don't know if this is supposed to sit like this or if it fell out of position when I pulled the carburetor up.  Anyway I put the spring back in what looked like a it's normal position (sitting straight up and down) and put everything back together.  The engine will run for about 7-10 seconds and than dies.  Sounds like it is simply running on the gas squirted in by the primer pump.  I also tried to gently push the flippy thing (governor?) either direction after starting the engine but the engine still dies right away.

FYI - I have not kept up on maintenance on this machine at all and have a fairly small yard so it gets used for about 30-45 minutes every 2 weeks for 7-8 months out of the year. (California) I did replace the primer bulb last year with some advice from my local small engine mechanic.  He is booked solid for the next 3 weeks as everyone in town is getting lawn mowers tuned up.  Sorry for the long story and if there is any more info you need just let me know.  If you think the problem is beyond me don't hesitate to say so.
Thanks, Gerrit

Answer
You need to visit the Briggs & Stratton website and use the parts locator and your engine numbers to look at the parts diagram for the carb/tank assembly.  This will give you an indication of how everything is supposed to be assembled.  It is likely that the carb needs to be cleaned (push a piece of tag wire through all of the internal passages and follow up with carb cleaner).  Make sure the screens on the fuel pickup tubes are clean and replace the diaphram.  There is no problem that is beyond a person with the motivation to solve it (unless you need special tools that are not practical to own for a one-time job).  If I thought people couldn't fix their own equipment with a little steer in the right direction, I wouldn't answer questions here.  Hope this helps.