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My engine would start and run good when cold but;
I just got through with a B&S old model twin cylinder about 18 hp that had the no start issue after the engine had been operated and got really warmed up. I could not shut the engine off after it was being used for mowing for about 30 min or longer or it would not start, just crank and crank. I could install a new set of spark plugs and it would be ok for awhile than same thing again. I could see little gas spit back up into the carb throat when cranking fast but I've found this to be normal on the Briggs twins when they don't start, even though compression is good and valves are adjusted correctly. (it's their nature to do such which is misleading when they don't start and cranking fast)
Spark testers and viewing both plugs indicated fire, compression good. I could let it set until it completely cooled of and it would re-start easily and fast. If it eventually started when hot it appeared flooded, usually had to be started with a full throttle hot, no choke.
Very hard on starters when such is happening also.
Here is an example of a clone mag that might be for your rig. Do not assume that the spark plug lead points forward, some are actually point backwards for the proper polarity. (China thing)
Also make sure you do not order anything that ships from China right now, might take 6 mo's to ever get to USA.
https://www.ebay.com/itm/595304-Ignitio ... SwHP1dy6IYI finally installed a new clone $15 magneto on it and two new plugs and it's been good every since.
I see your is a single cylinder OHV. I would consider just installing a $15 clone ignition coil and a new spark plug and give it a go. Instead of spending $60 on the genuine B&S mag) I'm assuming you have re-checked and made sure your valves are still sealing good after your lapping them. I've had good luck on the cheap clone mag's when installed on Briggs engines.
I've tried the Napa Auto supply $70 2 year warranty Briggs mags and had them fail in and out of warranty. (usually out of warranty, so I just started testing the cheap clones with good results. Be sure you do not install it upside down, some Mag's have a very faint UP or this side UP on the plastic coil and the kill wire tab and/or the spark plug wire may be pointed the opposite direction from the mag now in use, therefore it's easy to just
install what looks the same and it's wrong.
I would not install a ignition switch just yet, just disconnect the kill wire at the engine block area so as to make sure the kill wire does not have any grounding up set (any high resistance for example that would weaken the spark) going towards the ignition switch. Just be aware If the engine starts with the kill wire disconnected you will have to apply choke if you want to kill the engine or have a wire extended off the kill wire to ground and kill.
My engine had a bad mag and I've heard rumors the mag getting weak when hot is not uncommon. You also CANNOT fully test the briggs pointless type magneto because of electronic hidden deep inside. The old points type coils could be resistance tested primary and secondary and also tested on a coil spark tester to get an idea, BUT I've seen quite a few of them indicate OK but intermittent or erratic on a engine, especially the outboard engine type points coils I have a Merc-Tronic coils tester and I've sdeen it test coils as OK but when placed on engine probably due to vib's the coil would get erratic.
Appears you had two issues with that engine, valves and now something else.
Make sure the cooling fins are clean and all the air shrouds are on your engine so as it's not overheating.
Let us know what you try
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