My Yamaha 15HP 4 stroke is prone to carburetor issues, ethanol is a direct cause of those problems. I only need to run a bit of ethanol fuel and I can be assured I will be tearing down the carb. This is a 15 yr old O/B, and wasn't designed to use ethanol. I've torn the carb down so many times that I've lost track, but I can do it in about 40 minutes.
The phase separation that occurs in ethanol creates an orange snot-like precipitate that occludes the low-speed jet and the engine won't idle, it won't transition from idle to operation without balking or stalling, and it always happens at the worst time possible. I avoid ethanol fuel like the plague and that helps. It seems some engines are more susceptible to the woes of crap fuel, older ones more so. As a full-time cruiser, I've had lots of experience with it!
I have installed a
Racor 025-RAC-02 on the recommendation of Stephen Lance (of Defender). This 10 micron filter has a aquablock element that prevents the phase separated snot from getting to the engine. It's not 100% foolproof, so it may not satisfy the "NEVER" requirement of the OP, but it's been effective. I tried using stabilizer in ethanol fuel with very limited success. Best approach is to avoid ethanol altogether, entirely possible except in MD.