Sting S3 flight for BBQ with power failure on takeoff roll

Flew from KLZZ to KSEP for BBQ at Hard Eight. On the initial takeoff roll had a power failure and engine stall immediately. Runup was fine right before that. Called the factory who explained it was likely vapor lock, it occurs in Rotax engines occasionally when using auto gas. There are many regional variations to auto gas, and if you use fuel from a cold region on a day when it's hot, combined with a long idle on the taxiway, the hot engine can cause the fuel can vaporize before it detonates in the engine, causing power failure. The solution was to shut down the engine and let it cool for 30 minutes, and it ran fine after that. It doesn't happen in the air because you have air and water cooling when moving, but on the ground the water cooling can sometimes be ineffective. We were ready to call it a day but my discussion with the factory convinced me to try it again.

[@walterrawdanik8077]

In my 350 hours with my Sting S4 I have never experienced full engine power failure like that. Having fuel return like to the tank is supposedly best insurance against vapor lock issues - I do have a return line but only to the gascolator , also I only use non-ethanol 91/94 fuel I source from same location. I did have a partial power failure once but it was due to a bit of tiny debris in the carb bowl but it was nowhere near as dramatic as what happened to you - kzbin.info/www/bejne/hnTQlYGkhNeLhcU

[@jasonausman]

I've been using 91 octane with ethanol, our local non-ethanol fuel is only 87 octane so I can't use that. It was the first flight after our week of freezing temps in Texas. That was actually the second attempt. The first one it stumbled but didn't have full power. I went back, did another run up which had no problem getting to 4000. So on the second attempt I was wondering if I could "power through it" and gave it more throttle as it hesitated. The result was the stall. I talked to Bill Canino, let it cool down for 30 minutes and it ran fine after that and the next day. I also had to sit on the taxiway for 10 minutes at idle before that, the plane in front me of had a cowling open, had to shut down, close it, and restart.

[@walterrawdanik8077]

@@jasonausman Yeah, Bill Canino knows his stuff and he has always been there with useful advice whenever I called so chances are whatever he says is most likely what actually happened. That engine stall looked very much like a typical fuel exhaustion stall ( which you can force by turning off the fuel valve in the cockpit while the engine is still running ) so it does really sound like a vapor lock issue. Anyway, hopefully first and last one for you :-)