From your description I doubt the valves were adjusted properly. Seriously, metal gets hot and cold and as it does it is considered a physical work upon the very metal itself. This can easily change a length, a diameter, a spring resistance etc. Nominally, these things are averaged out and all works inside the allowable slop factor. But sometimes you get one that is on the edge of average and settles in just over the line.

One of the most useful bits of information I was ever given about gas engines is that they are not gas engines using 1 part gas to 13ish parts air, but rather air engines using gas given that air is the main compressible oxidizing agent. And sure, I would like space quality metal alloys on my machines and further, I would titanium bodies utilizing carbon fiber for max performance, with F1 telemetry fo robotic cutting and self reporting maintenance capacity, but they want more than I am willing to pay. For 3500usd you can get, today, a robot mower from Husqvarna. I like looking at my grass. If not it would be astroturf.

And as far as gas types go, and timing issues, low octane may combine to marginally retard the starting action via premature detonation. I run 89 octane because the Stihl guys recommend it for their gear and I find it works well in my Z71. I want the gear to do work for me, not the other way round.

The root cause of this no start condition is poor quality fuel compounded by owner neglect . Any experienced small engine owner realizes fuel must be treated and valve lash inspected routinely . As far as Briggs yes they have good and better quality engine models . However the basic preventative mtce remains . You do not run today's engines for a weekend then leave it for a few mths with untreated efuel . The beginning of this season valve tappets should have been gapped . Anyhow all I have heard from the op is gripe , rather then answer the simple questions requested , apparently just a whiner with little working knowledge of engines bent on bashing Briggs . Tricky keep the practice of 89 octane , this is the recommended rating for most 4 cycle air cooled small engines . 93 + octane burns much quicker and violently and long term can cause internal damage to these engines ! P.S. Like your air pump mythology !

Not a myth! The guy teaching the class had a masters in mechanical engineering. He worked for Alabama Power.

And I am sad to report that high octane gas burns slower, not faster than low octane gas. I apologize for changing your religion.

It is this retarded wave front that helps poorly set timing allow a start on a marginally wrong valve setting. A more violent burn from el cheapo gas would produce earlier pressure, and we are talking small margin here.

If you want to have a good time with OP, take his 2 cycle statement about the percentage of oils and do the math. Say 2 ounces oil per 128 ounce gallon of gas. Thats 1 to 64. Sure they can call for more but go with it. 2/128=1/64=.5/32=.25/16=.125/8=what? - roughly 1.5% oil to gas and he claims it to be a known problem instead of a known solution to lubrication in a 2 cycle?

Just sayin a 50:1 recommended ratio which is common is 2% oil.

I got you fam

Not comparing apples to apples within octane comparisons friends . High octane fuels are inherently used for high compressions engines to prevent detonation or engine knock . This fuel burns quicker and hotter than lower octane fuel at atmospheric conditions . However under higher compression is more able to resist ignition and therefore prevents preignition on regarded timed performance engines . However within low compression small engines it can burn aggressively out of the flame kernel of the combustion camber and cause servere valve and piston crown damage (demon heat) . Therefore the manufacturers recommendation for only 89 max octane rather than Sunoco 94 . As for the 2 cycle senerio , I routinely run Amsoul Sabre @ 100\1 ratio on all my 2 cycle units saws , blowers , trimmers etc that's 1 ounce in an imperial galone (4.5 litres) . Anyhow a little off the topic Bro . Wonder if the op has confirmed spark yet ?

No idea, but I def need you to describe me a test where I can see your octane theory in action. Bonus if things break, blow up or burn of course. I might even share video! Its just luck that my 89 choice has worked out then, but I have no compression tester, since I am not a mechanic by trade.

I had one of those Simplicity tractors until about '99, had no use for it and gave it away to someone who could use it to cultivate their garden. Original B&S engine, little balky at starting, but not too bad.

IMHO, in addition to the ethanol "infected" fuel we're forced to buy, the non adjustable "EPA" carbs are a major culprit in small engines today. I remember when you could actually adjust a carburetor, even take the needle screws out, etc. A relatively minute piece of crud can kill an engine, in the old days, open up the adjusting screw and it would blow on through. Worst case, tear down the carb and clean it, even worse case, rebuild it for a fraction of the cost of a new carb. Now, invest in a set of welders tip cleaners and get familiar with taking the cab apart-as far as you can anyway. Not uncommon for a replacement carb to cost 60-70% of the cost of the push lawn mower it's attached to today. Planned obselescence (sp?) anyone?

Yep definate OEM inferior carbs today . The old Tillotson and Kiehien of old where twice the carb then the junk supplied today on many small engine units Exmar !