What type of carb and by loading up what do you mean exactly.
If it needs a timing chain i would bet that is part of the issue. If the cam was replace they would have put in the normal timing chain as well. Are you sure its retarted or does it just call for one.
I would get a good double roller stright up chain and be done cam is probably not the issue. I would look at the plugs first if it doesnt have any bump at idle i would assume its not a bigger cam. Small enough cam to not bump will pull hard right out the gate. Unless its poorly designed. Sometimes the ends are stamped so you can read the numbers without removing.
I would look at the carb and the plugs for loading issues. Maybe little more timing at idle my help smooth it over. Hotter plugs can help prevent fouling form carbon but from oil you got ring issues.