18.5 hp Briggs & Stratton putting in rocker arms back, one goes in to far?

SOURCE: Briggs & Stratton Briggs Stratton Intek V -

these are common for doing this ,if you dont want to pull it down and hone the cyl. then i would use a heavier oil say 20w/50and that will probabley solve your problem

SOURCE: my 25 hp briggs is smoking and leaking oil. it

if the engine is ran quite a lot evey year the valves muct be adjusted. If not it will cause a head gasket leak which it sounds you have

SOURCE: 18 hp briggs & stratton intek i can get it

Check the choke, if that doesn't work the old gas may have left residue that is plugging your ports.

SOURCE: I have a Briggs & Stratton Intek V-Twin 20 on

This does not sound like a head gasket issue. Your description indicates fuel flow issue. Items involved are fuel filters, fuel itself, and the carb.

SOURCE: briggs & Stratton 18 hp v-twin engine surges

I put a new carburator kit in a Briggs & Stratton 18 HP Twin. But did not replaced the needle nor the new seat that came with kit, because I did not know how to remove it and did not to damage it. now the gas over flows