gw, I had a similar problem finding the button on my 7245 - simple answer is there isn't one - it's automatic. Now I just plug in the heater, prime it just before I turn it over and it fires up like a charm.
The only thing I did find was that the engine seemed to run at higher revs for an extended period of time - it may just have been because it was taking a long time to warm up (my temeprature gauge is broken so can't be sure).