Small Engines (Lawn Mowers, etc.): Lawn Mower Surging, briggs and stratton, adjustment screws

Question
I have a Yard Machines Lawn Mower with a briggs and stratton engine.  The mower is about 2 1/2 years old.

4 HP 21" cut High Wheeler Rear Bagger
Model #11A-544CO62  (O may be 0)
Engine # 10A902 2189 B3 01081754

About three months ago I was having trouble with it surging really bad.  I did everything I knew to do with cleaning the air filter and all, but nothing seemed to matter.  I ended up going to a small engine repair shop and they told me that my carberator probably had something in it and needed cleaned or replaced.  He suggested that I replace it since they are not easy to clean.  I replaced the carberator and the engine ran great once again, just like when it was new.  I also at this time replaced the spark plug and air filter.

Now.............

Just a week ago, about 3 months of steady once a week mowing the engine started doing the same thing again.  I have not had the air filter off during this time so I don't know how anything would have gotten into the carb.  I thought maybe I had some bad gas so I dumped all the gas and went and bought new gas and it still did it.  I took the air filter off and it still runs the same way so it is not an air filter issue.  I finally took the tank and carb off and completely dumped all the gas, I looked to see if I could noticably see anything and I cannot.  I have checked everything I can possibly think of.

I have now taken it of and on about four times, and the engine now starts off surging and then settles in smoothly with a really high idle.  It will idle high for some time and then start surging again ever so slightly when I start to mow with it.  I do not see any idle adjustment screws anywhere on this machine and I have checked the springs to make sure they are connected correctly (they are to the best of my knowledge)The engine is now idling way too high and is still surging, although not as drastically as when I started this morning.

I am lost!!  I would guess that there is some kind of obstruction in the carb but I don't see anything and don't know what further to check.  The butterfly seems to move freely, and everything seems to be sealed.

Thanks in advance for any suggestions.

Tim

Answer
Hi Tim,

Usually, surging is caused by a faulty or weak governor spring, located on the carb linkage.  Replace that and if it's still surging bring it back to the shop, even though some time has passed and ask them to correct the problem.

Let me know how you make out.

Michael

Unfortunately, I will be on vacation tomorrow so you may need to continue with another volunteer.