Unleaded like the name states, has no lead, but it does contain other additives. In a pinch, unleaded was used by me, and it worked. A little smokey on start-up, but ran well when warmed up fully. Not a wise choice because of the additives. Unleaded produces poisonous combustion by products and cause nasty deposits to build up inside the vaporizer/valve assembly. It may also effect your seals. As soon as suitable fuel was available,(naphtha from a hardware store), I swapped out the gasoline immediately. If I had a choice, I would NOT use unleaded.
I'm not certain if you have any experience with this stove. When I was 40 years younger, my scoutmaster loaned me a Svea stove. I didn't know how it worked and I went without cooking that rainy weekend. Since the stove has a built-in cleaning needle, the jet it is probably already clean. This stove is self pressurizing, so it must be primed or pre-heated. This is done by placing alcohol, priming paste, or even a small amount of the stoves fuel (coleman fuel or other white gas) in the small depression in the top of the tank where the burner is screwed in. By heating the top of the tank and the burner's valve assembly, the fuel expands and pressurizes the tank. At first the burner will sputter and flair up a bit, but as the stove warms even more, it will begin to burn cleaner with a strong blue flame. It will also be kind of loud compared to a butane stove. Seems like more trouble than it's worth for a novice, but this stove will work when a butane stove becomes a paper weight.