It was hot and high, 87 and 8300', and this morning when I went to restart, for the first time in 2400+ hours. it wouldn't. I fiddled with it long enough to consider the possibility of running the battery down, so quit while I was ahead. I opened up the cowl oil door, it's on top, and while waiting 15 minutes the sun also went behind some clouds. Then, the restart went as normal.

Nothing has changed with my fuel system, and I don't plan to tear into things looking for a problem, I might create a new one. One factor, and why I'm posting about this, I was parked on a slope steep enough to need the parking brake, nose high. I plan in the future before getting out to kick it around nose down, so just a tad more head pressure on the mechanical fuel pump. I failed to remember I have a fuel pressure gauge, one of the displays of my GRT EIS, and never looked at it during the non start now I wonder what it was reading.

A couple other things.... I need to get ahold of Earth X and ask them about the possibility, if ever needed (not this time, the battery remained very strong), of using my jump start battery pack thingie I've taken to packing along lately. Cell phone charger, bluetooth charger, flashlite with signal mode, it has it all and is light. It was on the hangar floor, and I haven't even been carrying the alligator clips for jumping a battery, but may start.

And, for the first time in probably 20 years, I had zero water in the plane, I ALWAYS carry some, even when flying in my backyard (where I was, about 20 miles away anyways), but I had robbed the plane for the bike ride I took the day before, and failed to replenish the plane's supply. IF the battery had run down, I would have been looking at a very long walk in mid 90's temp, Murphy's Law strikes again. THE ONE TIME I DIDN'T HAVE WATER, I CAME VERY CLOSE TO REALLY, REALLY NEEDING IT! I did have a pilot friend on standby, with water, and the plan was to have him air drop me some before the hike, but that would have meant waiting an hour or so. I'm never flying without water again, and always parking nose down (unless it's too steep obviously) is hot and high.

Never thought of vapor lock with carbs but I don’t think about many things.

Could be that this situation is what they had in mind for the electric fuel pump with the later kits. Usually see 4-5psi fuel pressure with gravity. 7 or so with pump on.

I read somewhere that most accident issues in experimental aircraft are fuel system related by a large margin. That really doesn’t give me a warm fuzzy. Glad you were on the ground.

I'd be more concerned if this was a newer bird. I was surprised it was that hot, but I have a good digital thermometer and the probe is out of the sun, though once 15 minutes went by with the sun now behind the clouds, it read 83. I've parked on steeper slopes, nose up, many times, at similar elevations, with no issues. Not many times though with that high of temps I'm guessing. As of now, without being flippant about the cause, I'm chalking it up to a perfect storm of temperature, vapor pressure of the fuel mix I had that day, elevation, the dew point, and the slope.

And just now, looking at this picture......I see another possible factor: I was parked cock eyed, off kilter to the right, and that is also the side where my header tank feeder line exits towards the engine, so exacerbating the previously mentioned factors. IF it happens again (and if nothing else when parking off kilter AND uphill I'll try and skew to the side favoring the header), I'd consider a boost pump but I already have a floorboard mounted aux pump I use for fuel transfer from portable containers, and before adding a third pump I'd probably come up with a way to make that pump also function as a booster, though I doubt the need will make that complication necessary, the less valves etc. in my fuel system the better. I'm actually more upset about having NO WATER on board then I am the hard start!

Was it pure gasoline and could it have been winter blend with a higher vapor pressure for ease of cold temperature starts?

About 5% or less E10 bought last week in Montana at a place on I-15 so has a good turnover I would think. Other 95% was EO bought just a few days earlier from a local, super busy place, so about as good as it gets I'd say.

CG

Correct me if I am wrong but I thought I recalled you mentioning that you did not have a fuel return line to the (or a) tank. That's pretty much the line from Rotax now, especially if using one of the newer pumps. Isn't vapor lock what happened to Jonas when he pranged his?

It does have a return line, always has. One time deal in 2400+ hrs, and it wasn't an inflight or on takeoff thing, just a hard restart.

My misunderstanding. One coughing event out of 2400 is pretty amazing actually