complete concurrence... dont get the requirements of two and four strokes mixed up...and ignore most of that drivel dragged in by a certain cat. close examination reveals several flaws here and there...
fourstrokes...ive always found ignition on any engine to be pretty irrelevant. yes, you can go too far both ways...advancing will reduce power, and make things hot...retard will reduce power but the thing will always start... but usually the factory is pretty spot on, even after doing major surgery elsewhere...which is a definite must on a four stroke!
it does help to get it in the right spot but its usually fixed for a reason... these days of CDI, nobody has to remove and readjust points... the manufacturer has spent the money on research and development...
not saying what engine it is, i can only assume that its a standard industrial engine...meaning, more than likely, a single lobe cam operating both valves.shame. not much you can do to the profile to improve it. can experiment, but each change affects both valves, and the curves they follow are NOT symmetrical! ie...you need a lab for conclusive results. old briggs and stratton, and other similar engines have separate cams...which can be modified
cam design is complex and theres things like "j3rk" and "float" and g-forces and strength versus load versus wear/life type things to consider... not for the ametuer to go making new cams! some engines, the parts are out there... most arent!
ports... removing manifolds will usually expose nasty casting flash, brutal square and right angled airways, gaskets that arent cut properly, the works... the smoother, and curvier the ports are, the better airflow will be, the better performance will be.
you can use jbweld/epoxy in the intake port to make it pretty... bigger is not always better!
exhausts... theres an ideal length pipe for any rpm with a given set of cams.
carb... most industrial carbs are junk...
slots...yep, should be obvious enough... the ones that the bolts go through to attach the thing to the cylinder...assuming its a cylinder mounted coil... move in direction of crank rotation is retard, against rotation is advance