My 49 3100 has a new gas tank, clean hard lines, new fuel pump w/glass bowl, rebuilt Rochester B and a glass bowl filter at the carb inlet.
After getting it roadable I've run Shell regular w/10% ethanol for approx 6K miles without problem. It sits Mon-Fri but gets 75-150 miles each weekend.
Both bowls stay clean and clear except the 2 times I used Marathon straight gas. Both bowls clouded up and my mileage dropped by nearly 2 MPG for those tankfuls.
The 216 avg's 12 MPG on stock 411 gears.
I went back to Shell at my favorite gas station. It does a brisk business which may contribute to the fuel being "fresher".
I've read several posts re. Marathon's fuel quality being questionable so it could have been a 2 bad batches of 100% gas that were a week apart but in my case my old 216 ran better on Shell's 10% ethanol regular than Marathons 100% gas regular....
