I've been running a Craftsman mower with a 10 HP Tecumseh on E85 for about 5 or 6 weeks with no problems. My carb had enough room for adjustment that all I had to do was richen it up with the load screw (not sure on the number of turns out, just turned it till it ran right). I can't quite get enough idle fuel. It'll idle but the gov. makes it surge a little from needing more fuel. I didn't advance my timing and I didn't notice any loss of power. It would probably have more power than gasoline if I did advance the timing. It's also noticably louder, which would probably change if I advanced the timing. I also have a 3.5 HP MTD push mower that I just made run on E85 the last time I mowed. It didn't have an adjustable main jet, so I went the old moonshiners route...choked it till it ran right, then made a stop for the choke at that point so it would stay partially closed all the time (I can still fully choke it for starting). It has an idle adjustment and I had to give it a little more idle fuel than with gas. It runs exactly like it did on gas, with noticably more power. I didn't think the choke method would provide the right amount of fuel at various RPM's, but it seems to run right at any RPM. If I have any problems I'll post here again, but so far everything seems fine!