one thing i suggest is when it dies, pull out a few spark plugs.
if they are wet then too much fuel is going in.
if they are nice and dry then either the right amount of fuel isnt going in, or its running lean..
if its running that rich, you should be able to smell it out the exhaust!
might want to also check to see if you got a nice strong blue spark out of the plugs, your coil might be starting to die or something, not giving a strong spark.
i dunno much about 4age dizzys, they got points? or electronic dizzy? if its points might want to either replace them (pretty cheap), or if its electronic then don't worry about it.