You could try pinching the fuel line gently enough with a clamp to shut off the fuel 30 seconds before you shut the engine off. That would tell you when you return to your first start of the day that you may have had the carb run over slightly if the backfire is gone.

I was going to suggest that the carb may be flooding as well. If the liquid fuel is leaking past the carb it also might be leaking into the combustion chamber and then the crankcase. Give your oil dip stick a smell and see if you detect gasoline.

The other test is to remove the spark plug and crank it over 10 or 15 times, to blow out that liquid fuel. Then insert the spark plug quickly and try to start it. If it starts well, then it was most likely flooding due to a leaking carb.

You might as well install a manual fuel shut off valve between the gas tank and the fuel filter, anyway. They only cost about $7 and take maybe 10 minutes to install. Use it during storage to prevent fuel leakage.

OP - one other thing - if you smell raw fuel when you pull that dipstick, best change out the crankcase oil/filter right away before running that engine much more. Crankcase oil diluted b fuel loses much of it's lubricating properties allowing rapid wear/damage...

Thanks for the replies!
Makes sense now. I usually end up pulling the plug and blowing out the cylinder to get it started. I get some misting blowing out. I just thought it was flooding do to choking.
I'm done for the season but I better go out and put in a fuel shutoff, or drain the tank less all my fuel runs out over the winter. I'll pull the carb in the spring. And do an oil change!

I'd run it once again, then do the oil change now...and inline shut-off valve....You may forget come spring...and crankcase oil, sitting all winter, may be really diluted with gas..,,And tag a note on it to fix the carb needle seat before using....IMO

Did some follow up and have pretty much ruled out it being fuel related. Oil is fine, no gas odor, and not overfull. Pulled the plug before trying to start and it was dry. turned it over a couple times no fuel in the cylinder. carefully inspected the carb and no excess fuel. Even unbolted it and checked with key on that fuel wasn't leaking past with fuel solenoid open. Put the plug in cranked it over and no start, then Bang out the exhaust.
Ok back to checking for spark...
Pulled the plug, laid it against the block and cranked the engine. It seemed pretty weak but even in the sun I expected to see more. I had previously set my magneto gap with a matchbook cover. So I went back and set it to .010, checked spark and was much improved. I could now see a steady spark. Put the plug in, pulled the choke, half throttle and after just a few spins started up and no backfire. Did a few laps around the yard, mulching up some leftover leaves and seemed to run fine.
So I'm going to let it sit a couple days and try it again. I expect it may start but I think there might be a problem either with the coil or the plug wire...
The condition of the wire, boot and clip connection to the plug all look good.
Can a coil go bad?
Can the resistance of the coil be checked?

The fuel solenoid has nothing to do with fuel flowing to the carb.
It has a pin that blocks the carburetor Main Jet. When energized, the pin retracts and allows the Main Jet to do Main Jet things.

I see, so it's just a fuel shutoff (at the main jet) should the float needle/seat fail?

I see, so it's just a fuel shutoff (at the main jet) should the float needle/seat fail?

No.
If the needle/seat/float 'fails, gas runs through the carb, into the cylinder(s) and on into the crankcase.
The solenoid just prevent running when power is removed to prevent afterfire.

IF you simply look at the carb, you can see the solenoid is nowhere near the float needle.

Ok so its not a faulty carb flooding the engine. It seems more that the excess fuel is getting naturally aspirated into the cylinder but not combusting. Then exhausted to the muffler where it eventually does with a bang. I'm leaning towards a weak or intermittent spark at this point.
Can a coil go bad where it delivers a weak spark?
Can the resistance of the coil and/or plug wire be checked?

Your idea seems plausible to me. Good catch. Coils can really be bad in undetectable ways though. Pulling the coil, maybe cleaning up the mounting surfaces and resetting again should it come back. Have you refreshed the spark plug? I assume that this is a 31 or 33" Intek?

Might be possible that inadequate fuel is getting into the engine through the carburetor.
Take a squirt can and put some gas in it. Squirt a couple squirts into the intake then turn the engine over and see what happens.

aeromaster - best use rattlecan carb cleaner in place of that ether starting fluid - small engines won't stand up to such...

your condition is typical of a failing coil...Especially if it is the Briggs opposed twin..A local mower shop will usually have several [used] coils, inexpensive, or perhaps even loaned to you..I think it's time to swap in a known good coil..Strange, as I researched your model Cub...shoulda had a Kohler Courage engine..Right?

Its a single cylinder Briggs
Engine model/type/code
31Q777/0305e1/040421ZE

My local shop has a lot of used stuff out back. I'll give them a try when I get back to it.
Oh and thanks for the tip on the carb cleaner...Don't need to make things worse

My Champion would fail to start and backfire through the carb. The problem was no exhaust valve clearance. Adjusted it and it starts fine now