Assuming that your timing is correct, with the engine off, take off the air cleaner assembly, look down the carburetor,inside, work the throttle open and close. You should see a stream of gas, like a water pistol. It should be steady not erratic. If there is no stream of gas the engine will bog when accelerating due to not enough gas too much air. Seems like a carb problem. Accelerator pump maybe not working or not adjusted correctly.