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  1. Default Gas Does Make a Difference!

    2 years ago, I took off the old Rochester 2 barrel from my '75 Grand Am. Project was to "make the car like it shoulda been ordered" from the factory. Stage 2 was to add true dual exhaust (yeah, I know they didn't have them in '75, but they SHOULDA!).

    Anyway, I found a date correct intake from a '75 Grand Prix. My neighbor who is a great mechanic and classic car nut too was helping me do the conversion. We ordered a brand new Quadrajet from a place he has purchased them before. When everything was completed and buttoned up looking "just like factory" including the factory stock 4 bbl air cleaner, it still didnt' idle well in hot weather. Really rough with the A/C on. The car also "dieseled' bad after shutting it off. We tweaked the timing, but it didn't help much. He finally asked what grade of fuel I used. Since it was designed in '75 and has low compression heads I said "87 octane, why?" He laughed and said that the newer gas is so bad, and in Minnesota we have that crummy 10% Ethanol, that when it's hot out, the evap point of the 10% "E" low octane is lower. He was suspecting the fuel was percolating. In cooler fall weather the car runs much much better. So this spring, I burned out all the old 87 octane and loaded it up with 92 premium. The car runs like a different automobile now! No rough idle, no dieseling. Yeah, it costs more to fill it up but it really made a difference. Just thought I would pass it on. Especially if you live in an "ethanol" state and have a mid '70's Poncho with low compression heads and pistons. Run 92 anyway and your car and you will be much happier!

    At least I can get away with true duals here since they don't inspect these cars.

  2. #2


    You might have had a bad tank of gas. I live in south Florida, so I am all too familiar with hot weather. We also have 10% ethanol, but there have been many reports of some stations having as much as 30% ethanol in their gas. That has caused problems with not just iold cars, but newer fuel injected cars too. I run 89 octane 10% ethanol in a 72 Chevy Cheyenne pickup, 350 4bbl with zero problems. I have a 72 Cutlass Convertible that I run 93 octane 10% ethanol. It runs better on 93 because it has more timing built into it. My 70 Bonneville is currently under restoration, but I have always run premium in that 455. It used to have 10.0:1 compression, but iI lowered it to mid 9's by going to larger chambered heads. I don't think the ethanol is the problem, because it is in all grades of gas. Unless it is more than 10% as it is advertised. Another thing is that ethanol attacks rubber parts like fuel line connections and the rubber parts in the carb. If the brand new carb was built before the move to ethanol, your fuel inlet needle will probably fail, as will the accelerator pump cup. You can get excellent rebuild kits from that are impervious to ethanol. Some parts store rebuild kits are complete junk when it comes to ethanol.

    Good luck with your Grand Am, which is one of my all time favorite cars. I bought a 1974 new (my first new car) in 1974. It was Admiralty Blue with burgundy interior and special order white seats, honey comb wheels and true dual exhaust. Some day I would like to buy another one, but they are really hard to find.
    Last edited by brown7373; May 16th, 2012 at 08:53. Reason: spelling

  3. #3
    Join Date
    Nov 2008
    Southeast MI


    Another thing to consider is that original hoses from the day are not compatible with today's fuel blends. So replace any original rubber hose with modern day equivalents, including the small one at the tank, the evap cannister, and any engine vacuum lines.

    Other things to consider with alcohol based fuel are:

    1. Alcohol requires different jetting vs. pure gasoline
    2. Alcohol fuels generate more heat and less power as the ethanol content goes up - so your water temp will go and your MPG will go down

    Rumor has it that the government wants to push E15 or high fuels onto the American public. The idea is that FlexFuel cars can tolerate it and it will slow or lower our dependency on foreigh oil (year - right). The problem is our classics cars don't handle this increase in ethanol well.

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