Modern Gas in Old Cars

As the gasoline in our cars becomes a cocktailed product of modern petroleum engineering, it seems that older vehicles (those owned by classic car aficionados and enthusiasts) are left to suffer.

We were reminded of this when a stunning little sprite (see above) that we’ve stored for many years starting having carburetor issues.


It is hard to tell from the above shot, but the base of the needle is getting gummed up. What causes this? Well many things can: Old gas and fuel tank contaminants to name two.

However you would not expect this to happen in a car in which we had just replaced the gas tank and fuel pump not even 8 months prior.

The issues here are two fold. 1) After speaking with a British car expert, it turns out that these roadsters are simply just susceptible to this… even when being driven regularly. 2) Modern fuel (the major culprit here) reacts with the metal and rubber in these old cars. This is primarily due to the high ethanol ratio.

We now have to take the fuel system apart and most likely have the vehicle undergo a major fuel system cleaning. However if you own one of these vehicles, here is how you can avoid this:

  1. Add a few fuel filters to the system. On a carbureted system, because its low pressure, you can add a series of fuel filters before the fuel hits the carbs. That way, it is much cleaner by that time, thereby reducing the likelihood of it containing contaminants.

  2. Run an ethanol free gasoline. This is kind of challenging and expensive if you use the vehicle everyday. But running a racing fuel like C12 can reduce the likelihood that your carbs will varnish because it doesn’t contain ethanol.

  3. Use a lead additive. These vehicles are old enough to be designed to run leaded gas. For environmental reasons, this fuel was phased out. You can buy a lead additive to add to your tank OR they make racing fuel with lead in it.

I will write an update for this post once we get this TR6 sorted!

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