To answer your question, no it won't harm the engine to run it on petrol alone.
Of more interest is that you say your engine is sooting up, which may indicate a rich mixture anyway, so running it on petrol may not help fix the problem.
If you don't want to buy your TVo in 44 gallon drums, try this mix:-
4 gallons paraffin
1 gallon petrol
250ml two-stroke oil (for the smell and upper cylinder lubrication)
1 pint of diesel (optional - mine doesn't like it)
There are other variations, but they are all about the same.
I think I'm right in saying that TVO has a slightly higher calorific value than petrol, so you can usually throttle back a bit when running on TVO - this helps economy a lot.