On Sunday I decided to do a little "tweaking" on the ECU fuel mixtures on my 13b powered SQ2000.  I had the larger 3 bladed Performance prop on, and just wasn't getting the rpm's I wanted, so I put the smaller dia/less pitch prop on and took it to the end of the runway and once I was lined up on the runway, advanced the throttle to wide open. RPM's were only around 5100, but I have flown it that way before, so I decided to go ahead and try to work with the mixture programming at 5000 feet.  Acceleration was normal, liftoff in less than 2000 feet, and started my climb. At approximately 250 feet, the engine started failing rapidly. I tried various throttle positions, with no improvement. Unable to maintain altitude. I immediately started a left turn, hoping maybe the engine would recover enough to just get me to 500 feet downwind so I would have a chance of making the runway. No such luck.  I was now heading back toward the center of the airport at approximately 100 feet and descending.  I wanted to land on the center turn-off section in the middle of the airport, but that would have me landing straight towards several parked aircraft and the main hangar.  Not the best option.  There is a newly paved area slightly to my left, where aircraft may be tied down in the future, but it was empty for now. I was out of options and altitude. I crossed the runway at less than 50 feet. I didn't want to land going across the runway, because the grass and mud I would encounter after rolling across the runway would probably flip the aircraft over. I headed for the new aircraft tie-down area, and attacked it at a 45 degree angle to get as much "runway" as possible.  I held it off until I was over the parallel taxiway, and landed on the parallel taxiway (the short way, of course) and with heavy braking, began skidding across the aircraft tie-down area. (See attached photos).  I knew I couldn't stop in that short a distance, but hopefully when I went off the other end of the pavement, I would not be going as fast.  The nose was dipped down at an angle from all the heavy braking, so I had a nice view of what was coming. Grass, mud and a ditch.  The aircraft kept slowing down, and as I ran out of pavement, I wasn't going all that fast. I probably only went 10 feet past the end of the paved area into the grass and came to a stop.  Missed the ditch by almost 5 feet !!!  No problem...that was fun !!! Just don't care to do it again.  I restarted the engine and taxiied back to the hangar, pretending nothing had happened. I don't know what to do at this point.  I don't care to have this much fun again anytime soon.  I'm torn between a carburetor and a Cessna.  Paul Conner