Briggs 18 hp v twin won,t stay running have cleaned carb and replaced filter gas is right govenor is working can see gas going in acts like no spark. replaced magneto- runs for a while but when trying

Clean or change air filter. Clean, gap or change spark plug. Empty gas tank add fresh gas with Stabil. When spark plug is removed pull rope several times to blow out cylinder. Spray starter fluid in spark plug hole before replacing spark plug. Clean outside of carb so choke works freely. Spray starter fluid into carb breather hole with air filter removed and try to start. if running replace air filter and cover. If no start disassemble carb and clean. If no start replace carb.

take spark plug out reconnect plug wire to plug touch bottom og plug against baremetal or bolt see if spark is present if not check coil or points

check spark make sure its bright blue but sounds like a dirty carb needle valve isnt opening enough not letting enough fuel in

Try cleaning or replacing air filter and check vent hole in gas cap to make sure it is still open. I would remove themuffler and spark arrestor and clean both with spray carb and choke cleaner.Brush out carbon build up and blow out if you can.Thank you.

I took the carb apart and found that it needed rebuilt, I installed the new carb and fuel pump kit and it runs great again.

Believe it or not, I had this same thing happening on our L120 John Deere. Turned out to be a plugged gas cap vent! At first I couldn't believe it but i resolved it with my air compressor. Now I always make sure the vent is clean and have had no problems since.

a couple other checks would be to dump the carb resevoir where the float is, water under the float could be accumulated and closing the fuel off, due to density. out here on the farm we never use the gas to the last drop from the can. also the linkage between the motor fan blade, (govenor) might have been connected to the carb incorrectly. or a bad switch interlock on the mower blade.
some briggs motors are hooked wrong straight from the factory, where the throttle linkage is concerned. ( and the little spring is pretty hokey too)

I had a similar problem with my 23 hp briggs. While cleaning the carb I found that the great gas we get today had eaten the seal around one of the jets in the throttle body causing it to fall out. Replaced the jet and now runs like a champ. Hope this helps.

have you checked the air filter,if that is clean I think I would replace the carb, diaphram.

carb needs cleaned or replaced