Double check your silencer and exhaust system for excessive back pressure (broken silencer core, bent exhaust, etc)
Remove fuel filter inside the Dell”Orto carburetor and look for debris.
Look for pinched fuel lines.
If the bog is a distinct “shut off”, then quickly accelerates as you increase throttle, you have a lean condition due to small pilot, to open on the air screw, or clogged jets. If the engine bucks or hops, or is very sluggish (but trying to clear out), the low end jetting is to rich.