Black/Dark Gas?

[rpoerner]

I have a crappy lawn mower that is old but it has a primer bulb on it and it always starts, but the gas after awhile goes from clear to dark black clear but it still runs. Any ideas what this is from?

 

[Rivets]

I would be checking for foreign debris in the tank. Wouldn’t be a bad idea to pull the tank and give it a good cleaning.