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Running 93 octane ethanol pump mogas I have been struggling with vapor issues in my CTSW for a while now, but I wanted to work through them as far as I could without asking for help. I ran this same fuel for ten years with no issues, and it came up after I changed my fuel system to include teflon-lined hoses. The symptom has been pretty consistent: intermittent power loss when the engine is hot and the deck angle is high. This means I most often saw it on takeoff and climb out, sometimes at very low altitudes (not fun!). The RPM would drop from WOT RPM (5200-5500 with the eProp) down to about 4000rpm, often surging up and down in 2-5sec pulses. Reducing throttle and deck angle usually allows me to fly at 4000-5000rpm and land. After this first happened I re-routed a fuel line to remove a potential vapor trap and the issue went away and was gone all Summer when it was hot so I assumed it was solved. Then I went to Tampa last fall to visit Bill Ince, and we were two up departing St. Petersburg and the issue happened again out over the water, two quick pulses and then it smoothed back out but we were both a little puckered up! The problem did not recur and we continued on the 15-20 miles back to Clearwater. Before I went back to Georgia I topped off with 100LL and had no issues going back home. After I got back home I went back to mogas and had no issues all winter, so I thought maybe a difference in Florida fuel blends vs Georgia could have been the cause, or just some bad gas in Florida. Carbs were rebuilt in March, and I flew until mid-April with no issues. The last few weeks it got warmer, but only in the 70s or so. Quite suddenly I started getting the vapor issue on every flight. I tried insulating all the AN connections on my fuel lines in case they were getting hot, but no joy. Finally I switched to 100% 100LL fuel and the problem ceased immediately and has been gone for several flights. I'm fine with running avgas if necessary, but I'm still a little confused over what exactly happened or changed. I checked my gascolator screen and did a fuel flow test draining out the tanks completely and there were no issues. My ideas are: 1) The new fuel lines are teflon, stainless braided, and with integral silicone firesleeve. It's possible the new lines retain more heat than rubber hoses and lead to increased chance of vaporization of ethanol. 2) Fuel blends have changed. I read that the EPA is working on changing the max ethanol in standard fuel from 10% to 15%...I'm wondering if suppliers have begun a stealth creep up of ethanol content or other additives. 3) I changed out my fuel pump when I did the hose change...perhaps my new pump is weaker than the old one? The old one was well past replacement age and was an older revision pump, but I never had this issue until after it got changed out. Maybe the new one is just a factory dud. 4) I had to make a new heat shield for my gascolator during the fuel system changes, but it's pretty much the same thickness aluminum material and the exact same shape as the old one if not slightly larger, plus it's more reflective so should bounce more heat. I guess I could beef that up or add additional insulation. Here's what it looks like: I'm certainly open to other ideas, recommendations, or wild speculation. I know Corey recommends a boost pump installation, and I'd do that if 100LL ends up not totally curing the issue, but so far so good. I miss the cheaper fuel, but it is more convenient to just pull up to the pump.

I think two areas where it tends to develop vapor issues are the hard downturn to the gascolator, and in the fuel pump. The fuel pump has the inlet on the TOP and outlet on the BOTTOM, which I think aggravates the issue. The hard rapid churning (prop RPM) of the plunger, and the fact that air has to move DOWN, makes me think it will foam up a bit before it is finally purged. The old pier burgs never ever had an issue and I really want them back.

We've posted numerous times about ethanol fuel and its properties. Plus you almost never see ethanol at its advertised concentration. Most states say up to 10% or 15%. People at my field with CT's have tested every batch of fuel for the last 15 years. We have up to 10% in AZ. The real number is 6 % - 7% and the highest we have ever seen is 8%. The people that jump up and down about ethanol being hydroscopic and water will come through the vents and saturate the fuel have no clue about the physics involved. I took one time in a CT and poured 6 oz. of water into a full tank and you know what happened. Nothing. Depending on the ethanol concentration it can suspend the water and just burn through the system. Is it as good as fuel without it, no, but it works and the engine just runs. Can heating a fuel line cause some vaporization, yes, but it can be mitigated up to a point. They use up to 23% in South America. One way to help reduce your under cowl temps is to use header wrap.