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Author Topic: Petrol vaporisation  (Read 840 times)
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davidwheeler
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« on: 31 July, 2018, 08:47:02 PM »

From time to time, in traffic in hot weather, my Nardi twin carbs suffer from petrol vaporisation and I have no option but to sit with the bonnet open until it all cools down.     I have a vague idea that later cars have a hole through the side of the engine compartment into the wheel arch (Huh??) to cool things down but I do not really want to take a grinder to my car.    Does the type of petrol make a diffeence?  I read elsewhere that Tesco 99 octane is less prone to this and also have a vague idea of fitting a fan and a tube to direct cooler air onto the carbs.  Anyone out there with any idea please?     The petrol pump is electric and in the boot so the problem is not there.
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David Wheeler.  Lambdas, Aprilia, Fulvia Sport.(formerly Appia and Thema as well).
GG
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« Reply #1 on: 31 July, 2018, 11:17:02 PM »

Having same issue in s.2 B20 with two single barrel Webers, and Elec pump is not solving this. I think its the gas these days.

One solution is to put a fuel return line from the carbs back to the tank to allow for circulating (and thus cooler) fuel. The idea is that the fuel is vaporizing from the heat at the carbs - you can check by feeling the fuel line just at the carb and seeing if it gets hot. 

We did this on a hot Aurelia with a Nardi setup and it worked wonders. Will probably try this on the B20. Consider for your Aprilia too.
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« Reply #2 on: 01 August, 2018, 10:12:49 AM »

I know its not a Lancia, but my pre-war Rover Sports Saloon also hates the hot weather. Luckily the mechanical fuel pump has a side 'tickler' but I also find, pulling out the choke increases fuel flow and helps no end.
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fay66
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« Reply #3 on: 01 August, 2018, 09:48:43 PM »

Having same issue in s.2 B20 with two single barrel Webers, and Elec pump is not solving this. I think its the gas these days.

One solution is to put a fuel return line from the carbs back to the tank to allow for circulating (and thus cooler) fuel. The idea is that the fuel is vaporizing from the heat at the carbs - you can check by feeling the fuel line just at the carb and seeing if it gets hot. 

We did this on a hot Aurelia with a Nardi setup and it worked wonders. Will probably try this on the B20. Consider for your Aprilia too.
I seem to remember lagging the fuel lines near the heat in my younger days.
Brian
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Dave Gee
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« Reply #4 on: 03 August, 2018, 07:03:25 AM »


  I think this is going to become a steadily worsening problem for all of us due to the increasing hot weather and amount of ethanol in the petrol. If you go onto you tube and put in 'vapour lock' you can see the petrol boiling in the pipe, where someone has replaced a section with clear tubing. Well worth a look.

My car has been having this problem for some time and I have carried out the following modifications:
1 had cast iron manifolds coated in heat retaining material
2 lagged the petrol pipe from the filter to the carb
3 fitted an electric fan
4 wrapped the stainless steel exhaust front section in heat bandage.

All of these modifications have had some marginal effect, but the problem still arises occasionally. My final effort is to keep the petrol circulating so it never sits in the pipe when the engine is running. To do this I propose to run a brake pipe from the petrol tank to the carbs going into the carb at the banjo fitting. The decision I now have to make is what size bleed hole needs to be made in the banjo fitting. I am considering around 40 thou. If anyone else has done this I would be grateful for advice. As I progress with this, I will take pictures and post them on a Flaminia thread at some point.
Dave
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lancialulu
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« Reply #5 on: 03 August, 2018, 09:05:15 AM »

I believe Series 2 Fulvias (you have one!) is about 1mm restriction (plus the return pipe adds some additional restriction to the return flow). On my Series 2 I did some experiments on regulating the fuel pressure and the car ran normally down to 1psi into the carbs (That included a blast down a dual carriageway) so it is down to pump delivery.
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will
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« Reply #6 on: 03 August, 2018, 07:17:52 PM »

On the B20 we have fitted a return system from the fuel filter  (which is in the engine bay)
back to the tank with 5mm od pipe . The car is fitted with an electric petrol pump in parallel to the mechanical pump and electric fan.
 i drove the car to the 96 club into Central London a few weeks ago on a hot day no problem with the electric pump on.

The M25 after the AGM could be a good test this weekend. 
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davidwheeler
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« Reply #7 on: 16 August, 2018, 09:43:23 AM »

No longer a problem Oop North but will try the return pipe idea in time for Continental tour next year.
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David Wheeler.  Lambdas, Aprilia, Fulvia Sport.(formerly Appia and Thema as well).
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