This concerns one of my older car but applies to all older carburated cars that despise modern fuels.

OK, it's 35C, I'm in a drive thru waiting for food and my 68 Ford starts idling rough.



I restart the car but it stalls again and won't restart. I coast down to a car park. This makes the second time this has happened with this car in the past 20 years. Last time it happened I was at the ATM at my bank.

I ended up having to have the car towed home. After it cools down it restarts. Hesitates a bit until the fuel bowel refills with petrol.

No, it's not the coil but vapor pressure building up between the mechanical fuel pump and the carburator.

I've never had this happen to my European cars although all of them are a pain to start when it get's above say 30C. My MGB has an electric fuel pump and seems to be the easiest to restart on a hot day after a heat soak for some reason. My 2CV is the worst.

But this stalling and not restarting problem seems to effect older American cars with mechanical fuel pumps when it get's really hot outside. It doesn't matter if your burning E10 or 100% or even 87/89/93 (RON+MON/2 method) petrol. It's something to do with the anti-pollution additives in modern petrol.

It seems modern fuels have a much lower boiling point than good old leaded 89 (RON+MON/2 method) petrol that were designed to run on back in the late 1960s.

I bought an electric fuel pump to go on the Ford because I've heard this will help. I'm not really sure how. Unless by using a 4 to 7 PSI electric pump provides more pressure to overcome the vapor pressure. Where a mechanical pump may not provide that as much.

Insulating the fuel line between the pump and carb is also supposed to help.

My 2CV has never vapor locked but it's probably doing the same thing as the Ford. It's a sweltering hot day, I shut the engine off, try to restart the car after it sits for 10 to 15 minutes and it's crank for 30 seconds with my foot to the floor.

Two things are probably happening. Vapor pressure is building up in the line between the carb and pump and the fuel pump is having to push all this vapor through the float valve.

Also as the pressure builds up, it overcomes the float valve, boils in the fuel bowel and wets the plugs.

So I got this crazy idea to over come this. I'm going to be trying it on my Ford and if it helps, I'm going to do this on my Citroen and my other cars.

Having dealt this turbocharged engines, I've used those mechanical boost controllers. The eco-friendly thing to do is to run a return line back to the tank but what about this.

Place a boost controller in the fuel line between the carb and pump and connect the port that would normally go to the wastegate to a hose and run it directly to the ground.

Set the boost controller to open slightly above whatever the pump pressure is. So if the pump puts out 3 PSI, set the boost controller to bleed off at 4 or 5 PSI.

That will push any pressure/vapors out of the line as the car is sitting in a car park or while idling. Of course it may puke some fuel out as well but the intake manifold on all my old cars are stained with petrol where they have been leaking. Probably where they have been boiling over during a heat soak or leaking throttle shafts.

Does anybody find anything wrong with this idea? Comments?

Here's the boost controller I'm talking about:

https://www.ebay.com/itm/NXS-MOTORSPORT ... XQHO9Rcan2

That sounds a bit too complex as a solution to me!

I can't see there being vapour in the fuel line! I can understand if the pump is a bit weak, that fuel may drop back down past the pump (also depending how full your tank is).

Check your pipe clips, as fuel lines can be a bit odd in that sometimes they won't let fuel out, but will let air in.

Consider a non return valve above the pump.

Edit
https://www.ebay.co.uk/itm/6-12mm-Inlin ... hq6jRM3M7Q

Usually, it just boils the fuel out of carb. Then, with mechanical fuel pump, you must to crank to have fuel to carbs, and it takes some time to do that. With electric fuel pump, just need to wait the bowl is full, before cranking the engine (if your car hasn't a device what controls the fuel pump, and doesn't allow pump to work if engine isn't running).

On my two carburetted cars, V6 and V8, no any starting problems if I remember to listen the fuel pump, and start after it can hear the sound alters -the bowls are full, without that there is a long, very long time cranking before the engine starts...

Can someone imagine why they moved to electric fuel pump with Range Rover at early days..? What I have heard from other RR owners, those what had mechanical fuel pump, they had a lot of trouble with starting hot engine on hot weather...

Air bubble in the fuel line can normally not been pushed away by the pump (vapour lock) Can test with cooling down the line with cold water pooring over it or insulate it with asbestos tape or an heat shield between fuel line and heat source..

One of the thing I'm going to do on my Ford and my 2CV is install a piece of clear poly tubing between the pump and carburator to actually see what's going on. If you scroll to about 1 minute on this video, it's showing fuel boiling inside the fuel line:

https://www.youtube.com/watch?v=cadNfSNi_Oc&t=226s

The condenses in the US anyway is installing an electric pump is supposed to cure vapor lock. Maybe because the mechanical fuel pump acts as a heat sink and by moving the pump downstream prevents this (or reduces this) from heating the fuel up after shutting the engine off or while idling in hot weather.

Or the mechanical pump doesn't really provide any real fuel pressure (like no more than a couple of pounds) to overcome any pressure building up past it. Where an electric pump can provide more pressure but not over ride the float valve.

The other condenses is installing a fuel return line. Still looks like sending heated fuel back to the tank is not going to solve this issue. Looks like after awhile it would heat all the fuel up in the tank. Especially if it's a high flow fuel pump. But fuel injected cars don't seem to suffer but they don't have fuel bowels either and push fuel at a higher pressure.

No doubt that fuel starts to boil inside the carbuartor after shutting the engine off but what baffles me is I can shut my 2CV off on a hot day, come back out 15 minutes later and have to crank for 30 seconds with the throttle to the floor to get the car started.

However if I wait say 1 hour and come back I can hit the starter and the car fires right up in less than 5 seconds. Which leads me to believe there is still some fuel left in the float bowel.

These makes me wonder if after 15 minutes, as the fuel in the bowel begins to boil , its being pushed past the jets, into the intake manifold and into the cylinders and wets the plugs. But after an hour, the heat from the engine causes any fuel in the cylinders to evaporate.

So the excessive cranking required with your foot on the throttle is just fill the cylinders full of air and dry off the plugs. Not to refill the float bowel.

So is the engine flooding out or the float bowel going empty?

That's just one of my theories.

On a side note. I actually had a fuel injected car that was a pain to start on a hot day. It was an 81 Fiat X 1/9. After some investigation I determined that the fuel line between the pump and injectors was not holding any pressure after I shut the engine off. As soon as I turned the engine off, the fuel pressure would bleed off instantly.

Someone had installed what I think was a Ford fuel pump instead of a Bosch and it lacked a check valve. Or the check valve in the pump was bad. This car had a vertically mounted fuel tank being a mid engine which may have aggravated the problem due to using a pump designed to run on another fuel injection system. So the pump the PO had used may have not been compatible with this tank. in other words it was designed to be mounted horizontally and not vertically.

I thought the regulator was supposed to hold pressure this but I replaced it to no avail.

The cure: Open the engine compartment lid between stops! The car would fire right up.

I don't know about the UK but British Leyand started installing electric pumps on MGBs in 1976 or 77. Mine has a Facet pump. I don't know if it's original. I would imagine it would have come with a Lucas.

This car has no fuel return line and has a Weber conversion kit on it. I've waited in drive throughs for up to 10 minutes idling on hot days and it has never vapor locked on me. This MGB also does not seem that particularly hard to start after it's been sitting for 15 minutes on a 35C day either.

I checked the fuel pressure one day on this car because there is no regulator on it and the guage showed 1 PSI of dead head fuel pressure! I was using a guage designed for a fuel injected car so it may not have been that accurate.

On my -76 Range Rover is also Facet pump, same type what is in Sm...

The fuel pressure on carb car, is low, about 1-2 PSI is ok...

Why circulated fuel in carburated car should be issue, but with injected shouldn't..? (as a sidenote, on my -95 Range Rover, EFI, there is a fuel temperature sensor on fuel rail)

Lucas made a lot of putting their stickers for example on Bosch EFI parts...

Do not over-engineer this issue...

my 52 landrover did already have an electric pump.

@turbofiat124

Sounds like your X1/9 had heat soak. The inlet air temperature (IAT) sensor was warming up with latent heat from the engine and causing the mix to go lean.

On the 2CV, dont forget, the coil can be an issue with hot starts.

And, forgot to mention. Do not compare total different cars to each other. Or, just try to think why Your 2CV doesn't use as much fuel as Your -68 Ford...

A different solutions have different behavior... (And yes, I have made that comparing also, but tried to explain why their behavior isn't same)