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How Come My Antique Vehicle Won't Run On This Modern Gasoline...?


I have been getting lots of questions lately about modern gasoline, and why it is causing antique vehicle owners so much grief. is a little insight into the problem.  As with most things you first need to understand the problem in order to understand the solution.

Two major things in modern gasoline cause us the most problems. The first one is alcohol. Most all gasoline sold in the United States contains ten percent alcohol as per federal law. Alcohol is a good cleaning solvent and will clean out all of the varnish and corrosion on the inside of your fuel tank. All of that "gunk" ends up plugging your fuel filter (you do have at least one right?) and eventually ends up in the carburetor where it plugs up main jets and the needle and seat in the carburetor. That leaves you walking.

Modern gasoline is also is a dry fuel so it will cause the gaskets in the carburetor to dry out and shrink. You experience this as a leaking carburetor. DO NOT follow your instincts and get the big number twelve flat screwdriver out to tighten all of the screws on the top of the carburetor. One of two things will likely happen. You will strip out the screws  in the top of the carburetor or you will crack the carburetor housing.

The alcohol in modern gasoline has more oxygen, which causes your engine to run lean. Sometimes adjusting the carburetor will help. Ideally you want an air fuel mixture of 14 to 1, fourteen parts air to one part gasoline. When you get down to below 12 to 1 you will experience poor idle stumbling upon acceleration and sometimes a high rpm engine miss under load. we understand the problem what is the fix...? First off stay away from the alcohol gasoline. Try to buy non-alcohol gasoline from a farm service station or in a station that sells off road gasoline, or sometimes it is called farm gasoline. Depending on where you live, places like boat marina's also sell non alcohol gasoline. Most small airports sell non-alcohol gasoline for  single engine general aviation. Ask around and you can usually find some.

Watch the gasoline pump you buy from and try and buy from a station that has an individual hose and nozzle for each grade of gasoline. The pumps that have just one hose for all the different grades means that you will get up to 3/4 of a gallon of whatever the last customer bought before you get what you selected. This is true even if you selected non-alcohol gasoline. If your tank happens to be only four to five gallons, the concentration of alcohol in your fuel tank could be pretty high.

If you see the transport delivering fuel at a service station drive on by...when they dump a load of gasoline into the underground storage tank it will stir up the sediment and water in the bottom of the storage tank and some will get delivered thru the nozzle. Modern fuel systems will filter that out... our older vehicles...not so much.

One of the simplest things you can do is add a pint of diesel fuel to ten gallons of gasoline. Modern gasoline has a lower boiling point to help with emissions and to make it a cleaner burning fuel. Modern fuel systems have 40 to 100 pounds of fuel pressure and we have 1 to 4 pounds in most cases. That is why you are experiencing vapor lock more today (where the fuel turns to vapor before it gets to the mechanical fuel pump) than you have for many years. The diesel fuel will raise the boiling point of the gasoline and keep the gaskets from drying out in the carburetor.  Accuracy is not critical a little more or less is ok. The engine will not smoke if you add the diesel. There are dozens more gasoline tech tips in " The Official Guide to modern Gas and Oil for Antique Vehicles" available in the technical publications section of the website.

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Since 1987, Fifth Avenue owner, Randy Rundle, has been making antique, classic and special interest vehicles more reliable and fun to drive.