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Author Topic: Air locks  (Read 288 times)
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Niels Jonassen
Senior Member
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Posts: 121


« on: 02 April, 2020, 08:33:31 PM »

Leafing through the October issue of Classic and Sports Car I noticed that Michael Powell mentions the air lock problems so well known to Aurelia owners. Omicron has solved the problem for him with a fuel pipe taking petrol from the carburettor back to the tank. He tells that rerouting the fuel line does not solve the problem. Well, for me it has worked. After having suffered from air locks a number of times in the most inappropriate places I fitted an electric fuel pump in front of the radiator and removed the mechanical pump. It stood the test one very hot afternoon in the centre of Turin. We drove for about fifteen minutes in a very slow queue. The water boiled happily, but there was no trace of air locks. I am not able to explain why this seems to work on our B20 and not on others. Incidentally Veloce has just published an very interesting book, Classic Engines, Modern Fuel by Paul Ireland. There are several chapters on air locks. 
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GG
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Posts: 428


B20 s.2, Appia C10 unrestored


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« Reply #1 on: 02 April, 2020, 11:21:24 PM »

We call this "vapor lock". If we are talking of the same thing, it comes from the fuel boiling due to the heat. Its a result of  modern fuels flashing at lower temps, and the heat build up, especially around the mech'l pump, the line and the carbs. If you happen to put your hand on the mech'l pump (at the motor) - its too hot to touch. Your solution is pretty good, by rerouting away from the mech'l pump and putting elec pump in front of the radiator, your fuel line got maximum cooling.

There are other answers:

One hot summer day, got caught  and was sidelined in the Appia with this problem. Wrapped some rags over the mech'l pump w some duct tape,  drenched them in water for some evaporative cooling - which did the trick.

Also the small return line back to the fuel tank worked well in a B24 we had. Its elec pump was by the fuel tank, and the fuel ran through the mech'l pump. The use of return lines was implemented by Lancia in some later Fulvias and also Ferrari c. 1970 in their US cars: the return line keeps the fuel moving more rapidly, and also, when the car stops, allows the heated and expanding fuel somewhere to go other than pushing by the carb needles and into the cylinders (very bad news). This way, the heated fuel can go back to the tank.... This solved our problems with a high compression B24 motor which got very hot in our summers. Also the B24 had a Nardi, which used reduced thickness spacers between carbs and intake manifold - so the carbs got much much hotter, especially after turning it off in hot weather.

Hopefully this agrees with other people's experiences.
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B20 s.2, Appia C10 unrestored
Niels Jonassen
Senior Member
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Posts: 121


« Reply #2 on: 03 April, 2020, 09:18:31 AM »

Thank you for using the correct word. I just translated from Danish. Let's hope that this will help some Aurelia owners. One of the times we got stranded was right outside a pub in York in England. So I ran in and borrowed a rag drenched in cold water and wrapped it around the carburettor. You are right. The carburettor gets very hot. All the other times we just had to wait.
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