I'm a certified maintenance mechanic for a large landscaping company and we own about 25 of these "Sprint" engines as we call them. They are very simple to fix and parts are priced low which is good, However there are some very common problems that occur regularly with these engines. The first is the diaphragms, to a home owner they will need to be replaced almost every year, for the commercial customers, it seems once a month is the going rate now. The second is, Briggs has changed the main jet in the carburetor pick up tube. The old jet used to be completely plastic and was manufactured as one piece, so as long as you kept the jet free of debris there were no problems, but recently on some of our new mowers, the main jet is now metal and it is pressed into the plastic pick up tube. What I have found is that due to vibration and jarring of the mower, the metal jet will fall out into the cup in the gas tank, causing the mower to spit and sputter due to too much gas getting pushed through the pickup tube. It seems everyday I have at least one fall out. The third and last thing is, due to vibration of the engine the carburetor and gas tank assembly will slowly cut a groove into the top of the Intake breather tube, so in my experience the intake tube will be replaced maybe a few times a year from heavy commercial use. None of the parts mentioned above will "break the bank" but compared to some other briggs engines, these require a little more attention when it comes to maintenance.
My engine sounds like it's struggling, not running smoothly. I think the carb needs adjustment and my manual does not provide any pics of carb. I can perform this myself, just need to see where it is in engine.
There are no adjustments to this carburetor. Make sure the carburetor is clean and free of debris, check to make sure your diaphragms are not hard/cracked/holes in them. And another recommendation is to drain the gas and put NEW FRESH GAS in it. I have seen stale gas come right out of the gas station pump, so don't assume that the gas is good.
These engines are found everywhere, and in my experience all parts are interchangeable from one engine to another. The only part that I know of that varies is that some of these engines are make with a mechanical governor and some are made with an air vane governing system. If you have a mechanical governor then as long as you get model numbers from another engine that has the mechanical governor, all parts will interchange. Same goes for the air vane type.
Can physically stopping the camshaft impact timing and can this be adjusted.
500 series engine is running rough; surging/almost stalling. Acts like a dirty air filter but persists when air filter is removed. Seems to get better if idle is increased...carburetor cleaning helped somewhat. Engine was stopped by encountering twine that wrapped around the camshaft. Twine was removed and engine restarted, but has run rough since this incident.
The timing on this engine is controlled by the Flywheel key. The key is located between the flywheel and the crankshaft. When the blade his something hard or gets entangled the key will shear for the sole purpose of saving your engine. I would check to make sure the flywheel key is not sheared. The second thing I would do, is check your main jet in the carburetor, it sounds like you have a fuel problem if it the engine flattens out when idle speed is changed. My guess would be that your main jet is sucking too much fuel and choking out the engine.