Oxygenated Fuel

By Joe Curto, College Point NY

Reprinted from Intune, published by Fourintune Garage, Inc., Cedarburg WI

Originally published in the Austin-Healey Magazine, December 1996


We had heard that certain color carb diaphragms used on the HD6 and HD8 carbs were breaking down when owners used the "environmentally friendly" (oxygenated) fuel which is mandated in many states and the southern counties of Wisconsin. One problem with the new fuel is that is has a shelf life of only one month. So if you are putting your car away for the winter, make the trip outside the areas that sell oxygenated fuel and fill up your tank with real gas.


If you are not sure what they are selling, ASK!


In order to oxygenate fuel, they add ETB (ether based product) or an alcohol/ethanol-based product. Both of these substances seem to attack the rubber in carb diaphragms, which can cause big problems. Prior to the new fuel, we used whatever color diaphragm was sent to us as a replacement. Not anymore! After tuning and adjusting our 100-6, I filled up with the new fuel and within less than one week, while driving home, the smell of gas was over-powering. Looking under the hood, the rear carb was leaking gas big time and pouring onto the hot exhaust below The leak was so bad that I brought tools home and did the rebuild there rather than risk a fire by driving another 15 minutes back to the shop.


In one case, the black diaphragm in the rear carb had shriveled, melted and been reduced in size by a considerable amount, causing a leak. This took only a few days to happen. We now replace them with the bright blue type that does not seem to be affected, though there are reports that the green ones do break down. Confusing the matter is the fact that not all black diaphragms are affected by the new fuel.


Rather than take a chance at this point, we use only the blue diaphragms. If you have either HD6 or HD8 carbs, check for a leak at the bottom of the carb, not the bottom of the float bowl. If you see any indication of a leak, it might be prudent maintenance to change the diaphragms before the problems worsen.


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