That is strange.  I had a lean burn on my '78 magnum.  I used ethanol on 
it also.  My gas mileage also improved.  I did have to replace the fule 
 (fuel) pump once and the fuel filter a few times until my gas tank was 
cleaned out sufficiently so the gunk wouldn't clog up my lines or the 
fuel filter.  I have been surprised as the response to "Ethanol" being 
bad for cars and gas mileage.  Have you tried modifying the carburator 
jets or adjusting the fuel feeding rate?  You might want to check your 
fuel.  You might be running "Gas-a-hol" rather than Ethanol.  My husband 
put ethanol in his '66 Plymouth Valiant and increased the mileage.  
Gas-a-hol is 10% alcohol and 90% gas.  That will decrease your mileage 
and eat your fuel system for lunch.    
    
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