I put gas (that has a chemical) for a weedeater into a lawnmower.

Can I still start the mower or does it need to be removed?

I put gas (that has a chemical) for a weedeater into a lawnmower.

Can I still start the mower or does it need to be removed?
You really want to remove it before starting. It will smoke like a mother and the oil mix can gunk up the fuel line. Even with emptying, expect it to smoke

Yes, remove the old fuel from the tank, lines and filter. Also remove the carb. Float bowl and remove the "wrong" gas from here as well. Then reassemble and try it again. Also, label your fuel tanks to help prevent this in the future. I personally use a 2 1/2 gallon fuel tank for my stihl products (mixed fuel). And a 5 gallon can for regular fuel. Try this and it is easy to always grab the correct fuel tank. And this is not as bad as you think. I know an older fellar that poured antifreeze into his fuel tank on a diesel powered massey furguson tractor, that was really bad.