4.75 Briggs will not stay running.

[jfulton50]

Took carb apart and cleaned with spray cleaner. Was afraid to put in bucket of carb cleaner. Replaced primer bulb. Cranked it up and it ran for a few seconds and if I bounced the mower up and down it would keep running but if I let it sit it would stop. Didn't know if there was a needle valve stuck possibly. Any suggestions?
Thanks,
John

 

[mechanic mark]

Post engine numbers from data plate, check spark plug & air filter for replacement, fresh gas in tank.

 

[bertsmobile1]

Crap in the fuel tank

 

[Rivets]

Viton seat swelled, not allowing enough fuel into the float bowl.