FlyingMonkey

Whoa, I didn't know the pipes could warp. I'll call you when I get a chance and our time zones line up.

Ha, same picture, different airframe:

Well, it was clear when I installed it last year during the hose swap. I hate to disassemble it and potentially induce leaks in that stack to re-check it, but I can if you think it's worth doing. Or is there an easy way to test that without taking it all apart? I think I'm going to wrap the exhaust and then get some fire sleeve around those lines on top of the engine just for extra thermal protection. When I do that I'll probably have to pull the lines and I can check that orifice then.

I found the header wrap kit and stainless lock ties in my hangar, I'll bump that to the top of the project list. When wrapping how much do you guys use for overlapping, about 50%?

Same until very recently...

Here you go:

I agree that the probable cause is something with the new fuel system. As I mentioned, I thing the new hoses might absorb and retain heat more. To be clear they do have a fire sleeve, it's just integrated into the silicone around the hose. But I do agree the old fire sleeves probably insulate the hose better. The header wrap is seeming like an easy enough thing to try. Shielding the hoses on top of the engine might be fairly easy as well. I think it all comes down to how much work I want to put into resolving this in the Summer flying months beyond "put 100LL in it and forget about it". I suppose I can just run 100LL for now and try some of these other ideas when the weather is too poor to fly. I can also easily experiment with mixtures of mogas and 100LL to see if I can just dump a few gallons of avgas into it every tankful as an easy fix.

Wilco, I'll snap one tomorrow. I thought I had one but can't find it.

Yes, I have drip trays installed. Good suggestion. It sounds like header wrap keeps coming up as something to put in place.

I have avoided wrapping my pipes because I have had exhaust cracks in the past and want to be able to see the pipes to catch problems early. But there have been no issues since you helped me out in Tucson and we set the exhaust correctly with no stress on the pipes like 8 years ago, so it might be time for me to revisit wrapping. IIRC I have some header wrap in the hangar already.

Thanks Corey I'll consider a mix. I admit it would be nice to keep the avgas to 30% or less to take advantage of longer Rotax maintenance intervals. I do have self serve on my field so that makes it easier. I agree the deck angle makes a big difference. Once the engine had issues, pitching down was often enough to clear it, but pitching down and reducing power always got it under control. At its worst even making a consciously flat, shallow climb out wasn't enough to avoid the problem.

I didn’t want to turn this into a Mogas v. Avgas argument. I don’t have anything against Mogas and ran it with ethanol trouble-free in hot Georgia Summers for a decade. But something has changed and I need to change with the situation. Fred I don’t think the new lines are poorer at insulating the fuel from heat. What I suspect is that the stainless steel braiding absorbs and retains heat, and potentially transfers it to the fuel and leads to higher chances of vapor formation. It’s maybe a distinction without a practical difference, but I just want to be clear about what I think is occurring.

I have tested my gas in the past and it was around 5% ethanol, I have not tested recently. I don't really want to run a fuel mixture because you then get all the hassles of avgas AND all the hassles of mogas, and save hardly any money on fuel. I'm only saving about 50 cents a gallon between 100LL and mogas as it is.

I imagine if I had a restriction, blockage, or wrong size orifice I would have the issue with both mogas and 100LL, right?