Engine dies after 45-60 minutes

[OldChipper]

I have 42 inch rider with a 18.5HP Briggs and Stratton 303777 twin engine. Been running great with regular maintenance. But lately it will run for 45-60 minutes and dies, as if it is not getting fuel. 1st time I thought no problem, dirty fuel filter, replaced it even through the old one looked OK, mowed about 40 minutes and same thing, so I cleaned the gas cap, made sure it was vented, same thing, checked the hoses, fuel pump, engine isn't hotter than normal, compression is okay, plug is new, oil level is okay still almost clear; checked on a carb overhaul kit, B&S 807962 kit runs over $120.00, must be gold or something. Could this problem be the carburetor, hate to spent that kind of cash if it doesn't help. Can a small engine vapor lock? I checked the fuel line to be sure it's not near anything hot. But can't say I ever heard of a mower vapor locking?? What am I missing, this has been a great running engine until now.
Not much on carburetors, would cleaning it good maybe help,. If so is just blowing compressed air enough to clean all the little openings, kind of worried poking a wire in them?
or could it be something else altogether.
many thanks!

this is an old 1997, 42" MTD Yard machine, B&S 18.5hp twin, 303777-1032-A1 96121111, hydo trans and not all plastic

 

[Mikel1]

When it does this will it start right backup or do you have to wait?

 

[bertsmobile1]

Pull the fuel line off the carb when cold and drain out a quaintly say 3/4 bean can or something that will fit comfortably under the carboy fuel line.
Roughly count out how long it takes.
Start to mow & when it gives you greif dothe same thing again.
If it is a lot slower you have crap in the fuel tank or a colapsing fuel line.