Briggs & Stratton Classic not running well. Carburetor broken?

Well, the air filter hold down screw HAS to be installed or it'll suck fuel out 
of that orifice..
 
Your diagnosis sounds correct, running too rich.
 
Do you have a large air adjustment screw on the pull starter side (on the carb)?
Turning it in clockwise LEANS out the mix.
 
If you can post your engine model #, it would help..
 
 
.

Hello and thanks for helping.

I can confirm:
The head bolts are tight.
I have repeated the test with the airfilter bolt installed, it is the same. I see the same pattern of fuel flying out of the main jet like shown in my video.
There are no adjustment screws on that carburetor.

I am not able to locate a model number for the engine. I think it is a 3.5 perhaps? (Despite watching a video from B&S showing the 3 locations of the model number.)
The mower is Rover.
I have pictures of the mower and engine sides but the forum does not allow me to upload them.

Hello,
I have since borrowed a complete tank with carb from a friend's mower.
I bolted it on, added fuel and it runs like a sewing machine. Despite his primer bulb not working. I do not see fuel flying and percolating from the jet like on mine.

I still cannot upload pictures or share links. Can a mid please fix that?
Here is another video:

youtu.be/0tEaa5rRF54?si=QVKOlBOB8SQSwfg9

So now what is the problem on mine?
I stripped it again.
It really all looks fine.
Any ideas greatly appreciated.

I am not so sure now.
 
That carb is plastic and only has bout 4 parts to it.
I did a lot more more troubleshooting by swapping parts from good to bad etc by elimination.
 
Interesting find: I eventually swapped the good carb onto my fuel tank and the problem remained!!
So now I had the good carb also spitting petrol and percolating simply because it was on my tank.
 
I could not find ANY difference on my (now bad) tank to the other good tank. Same holes, same surface, not warped, nothing different.
 
So Lastly, I swapped the membrane and gasket from the good tank to my "bad" tank with the good carburetor.
 
The problem went away.
The cause of this problem has something to do with the membrane /gasket combination.
I do not know what. However, the thickness of the good membrane combination is 0.8mm thick and the bad combination is 0.43mm thick. 
So my mine is thinner to almost half of the good one. Mine is new though and I then checked my old one and it was the same. 
I am now wondering if the membrane material on mine  is letting some fuel through, causing this problem.
 
Surely someone out there has encountered this?
 
To summarize:
1) The engine recently started running badly, running just like I video. I have had the mower for 16 years.
2) I ordered a kit and replaced the membrane/gasket and cleaned the arb and tank.
3) After this, the engine ran as badly as before and I could not find anything wrong with the carb etc. I started this thread.
3a)I observed and videoed fuel spluttering about from the main jet or somewhere near it.
4) Swapping the tank/carb with a borrowed really old one fixed the issue.
5) Discovered that the issue seems caused by the membrane/gasket combination as swapping that for the really old borrowed one fixed the issue - or so it seems.
6) I still do not know what the actual cause of  the problem is.
 
Best Regards
Bernt
 

Aftermarket.
Why?

So what can be wrong with the actual parts I have?
Yes, thinner than the old one.
But I just went an hour ago and bought a OEM gasket kit for $25 and measured the thickness. It is also as thin as the aftermarket one. OEM now is not same as OEM way back either.
 
I am still keen to find out what the actual problem is in this case.
I am surprised nobody here has encountered this issue before.
 
Best regards
 Bernt

What if I told you that 2 people, who are not idiots, have had several looks and comparisons and the parts look exactly identical, no faults visible, except for an extra 1.15mm jet in the input hole under the primer bulb of the good one. It is not clear if that should or should not be there. It was definitely not in there and not lost during disassembly.
 
So many things are simple in principle but then in practice, that is not always the case, when a problem like this presents.
The simple solution is to replace the tank and carb, which is what most would do, but that is cheating!