Several things can do this, most commonly is the accelerator pump on the carb. Pull the air cleaner/spark arrestor and while looking down the carb throat, have someone operate the throttle. This can be accomplished running or not. You should see a strong stream of fuel squirted into the engine. The second item would be to check the timing to see if it's set correctly, and if it advances correctly. Sometimes the centrifugal advance mechanism can get stuck. Low idle speed can also be a consequence of retarded timing as well. There are other items that will give you the off idle bog, but these two are a good starting point. Let us know what ya find. Good luck.