Blue Fuel?

Howdy!
I've got some blue fuel in a 4 stroke tiller. How do I tell if it's 2 stroke fuel or not. Someone rented the machine and now it's got this stuff in it.

The test I use is to put some of the fuel on a Kleenex and allow it to evaporate. If it leaves an oily residue it is two cycle mix. Works for me, but you may want to just dump it out and start fresh. The little left in the unit will not cause a problem.

The worse thing that will happen will be it will smoke.

The Kleenex trick sounds pretty cool thank you, I'll have to remember that for in the future as well.

ILENGINE- This is what I've understood in the past, but I am no mechanic. A couple of weeks ago though a customer brought back a brand new generator because it was surging. We ended up replacing the carb after some other attempts to fix it, and it still didn't help. My Boss noticed a lot of oil in the air filter, so he blamed the guy who sold it to the customer because he thinks he put the wrong type of fuel in it ( we put a little fuel in the unit and fill it with oil and start it before the customer takes it.). The top of the piston has some dark brown gunk on it. Would using 2-stroke fuel do something like that?
Sorry for the noob questions. Both of our mechanics quit and I'm having to fill their shoes you might say.

I can see where the oil in the 2 cycle mix in some of the new epa carbs could potentially cause a lean run issue, but should be temporary when new fuel is added clearing out the oil mix. I suspect the problem with the generator that you mentioned was due to the customer or the person that added the fuel initially has went bad or was marginal to start with, and the oil in the air filter is due to the customer tipping the generator on its side when hauling or unloading the generator from the vehicle.

I have seen pressure washers that have been tipped over that had Honda engines, and the oil will pool in the carb and actually fill the fuel bowl full of oil. Some of these new engines are really and I mean really fuel quality picky. I have gotten to the point that if a piece of equipment comes into the shop with a no start situation one of the first things I do is dump the fuel. Every piece of equipment that has come into the shop this week has had urine colored fuel in the tank.

Yeah we thought the oil might have come from it being tipped as well. We're definitely not giving up on it yet, my boss is just going to take it to a place that deals with Honda's more.

I just had someone come in within the last month inquiring about a machine he had that wouldn't start. I asked him if he had been using old fuel and he said " No, I've been using it all summer and it's been working fine!"