we have multiple engine models in this thread. Specifically
1998 Briggs & Stratton engine model 12F702, and 1781F1, code: 98081758.
To get correct answers the best thing would be to correctly list the model, submodel, and serial then verify it before hitting post. It should be something like 12F702-0606-01 etc., and not just 12F702 or 1781F1. List all the numbers. Get a rag and wipe down the serial number to read it clearly.
I have my best luck getting parts and part numbers thru
https://shop.briggsandstratton.com/ There is a parts lookup tool on the right side of that page in a red box. They will list each of the engines in that say 12F702 series if that is the engine. The date codes are listed if multiple parts were used. Be sure you understand Briggs and Stratton date codes before you order a part. 98081758 (if that is the serial) would be first 2 year of Manufacturer or 1998. Next two are month 08 is August. Next two are day of month - in the serial above it would be the 17th. So that engine was born on August 17, 1998. The last numbers are the factory, which I think is the Poplar Bluff Missouri plant.
An engine with a serial of 01012058 ( which is in 2001) is newer than one reading 98081758 (which is 1998). So when a part offers two parts, one for up to 071210 (which is 2007), and one 071211 and later, an engine with the 980817 is the first one because it is older. Don't just look at the numbers as a sequential number, 1, 2, 3 etc..
I am still betting on the O-ring being loose where the carb attaches to the intake manifold. And maybe the air filter base needs a new gasket or part. Can also be debris in the fuel tank. If you pull the carb off, take photos of how the linkage hooks up first.
