If the passage from the secondary well is plugged it will do the same thing. First time I found this was rebuilding a side bowl carb like this one. This will plug the cap jet. I have heard timing gears make this kind of noise as well. It would be worth it to pull the side timing gear cover and inspect it. Marco's timing diagram is dead on and will take care of your timing. If you have original points once the rubbing block starts wearing it will quickly close the point gap and add to your troubles.
When it comes to carb problems take a few minutes and review the operation of the zenith carb from this excellent site.
www.modelabasics.com. Great animations that really show you whats going on.