I see you have replaced the fuel filter, and you are running at, about 30 mph. It sounds like a fuel supply problem. Ok, the easy things first.
The fuel pickup in the tank might be either clogged or the screen that filters the fuel might be clogged. Check ALL of your filters
The fuel pump, ( if it has one) might be broken or worn out. Usually when an engine runs on a slow or medium speed,is OK, then when the demand for higher speed is needed and it either, cut's out or stalls, it is a fuel supply problem. Usually it is the filters.
Be sure to check that the vacuum hoses from the engine to the carburetor are connected and not cracked so they are not leaking,causing the internal carburetor fuel pump not to work.
The fuel pickup in the tank might be either clogged or the screen that filters the fuel might be clogged. Check ALL of your filters
The fuel pump, ( if it has one) might be broken or worn out. Usually when an engine runs on a slow or medium speed,is OK, then when the demand for higher speed is needed and it either, cut's out or stalls, it is a fuel supply problem. Usually it is the filters.
Be sure to check that the vacuum hoses from the engine to the carburetor are connected and not cracked so they are not leaking,causing the internal carburetor fuel pump not to work.