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DB18 fuel vapourisation

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Mark Bullen
Posts: 219
Joined: Mon Feb 15, 2016 1:07 pm
Location: Wiltshire

DB18 fuel vapourisation

Post by Mark Bullen »

With the hot weather has come a new phenomenon. Car runs at normal temperature no problem but on stopping for fuel, car restarted no problem but then only travelled a short distance before cutting out. Only cure was to hand prime the fuel pump and then ran no problem until stopped again for a few minutes and had to repeat. My assumption is that the heat soak vapourised the fuel, albeit enough in the float chamber to start and travel a short distance. Has anyone experienced similar problems and any solutions? The design of the fuel line is that runs around the back of the block and up over the inlet manifold so always heated, fine for the winter but maybe not ideal for the current temperatures.
The positive outcome was no one following got cross and even had offers of a push - which I politely declined.

Peter Grant
Wise Man
Wise Man
Posts: 503
Joined: Thu Mar 10, 2016 10:02 pm
Location: Sydney, Australia

Re: DB18 fuel vapourisation

Post by Peter Grant »

Hi Mark,

I had pretty bad vapour lock on my DE36 and found that some improvement was had by lagging the fuel line with a good quality self adhesive foil type insulating tape.
It hasn't cured the problem but it is better.

Cheers
Peter Grant

ranald
Helpful Person
Helpful Person
Posts: 485
Joined: Sat Feb 13, 2016 8:21 am
Location: North Wales

Re: DB18 fuel vapourisation

Post by ranald »

Mark, The same subject is being discussed under heading "vapour lock Daimler V8 250". It is worth a read. Hope your problem can easily be resolved. Regards, Ranald

John Hitchins
Site Admin
Posts: 244
Joined: Mon Feb 08, 2016 10:52 am
Location: Wellington Somerset

Re: DB18 fuel vapourisation

Post by John Hitchins »

Mark have you got the carb heatshield? easily available if not.

Chris_R
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Posts: 662
Joined: Wed Feb 10, 2016 12:48 pm
Location: Twickenham

Re: DB18 fuel vapourisation

Post by Chris_R »

I don't think it's a problem in the carburetor, I don't think a heatshield will solve this problem. As Mark says, he was able to restart immediately and drive a short way before cutting out. This indicates there was still fuel in the carburetor to run on for a short time. I also don't think it's a problem of fuel line lagging either. If the pump still had fuel in it then it would pump through any vapour in the fuel lines.
I had a similar problem twice on a Rover P6B 3500 that I used to run where at idle, especially after a long run on a hot day, the heat could evaporate the petrol in the fuel pump. After pulling away again a few hundred yards down the road the engine would die after the carbs used up their internal reservoirs of fuel and the pump wasn't pumping any more through. I remember one occasion when it happened just after joining the M4 in Wales and I stripped the pump at the side of the motorway, found it empty, found nothing wrong, re-assembled it and drove all the way back to London with a caravan in tow with no further issue. As I recall it was a known problem in the Owners Club and the only real solution to the problem was to fit a small electric pump to re-prime the main fuel pump if it happened again.

Marcel Renshaw
Man of Many Parts
Man of Many Parts
Posts: 673
Joined: Fri Feb 12, 2016 8:44 pm
Location: Derbyshire

Re: DB18 fuel vapourisation

Post by Marcel Renshaw »

I would suggest re route the fuel line so it doesn't run across the back of the block and along the exhaust manifold.
I also wrapped the exhaust manifold and down pipe to reduce under bonnet temperature.
Running better now.

qantasqf1
Posts: 299
Joined: Mon Mar 07, 2016 10:13 pm

Re: DB18 fuel vapourisation

Post by qantasqf1 »

Here in Oz it gets hot! This means vapour locking is a chronic problem, especially with the DB18. With the less-than-brilliantly positioned exhaust manifolds immediately below the carburettor/fuel line I've found that when the car stands for about 20 minutes or longer there's no problem, but shorter periods (like filling up at petrol stations) there definitely is. I found the way to deal with this without spending any money with (and no guarantee of fixing the damnable thing) is to open the right hand bonnet after switching the ignition off. A bit of a pain in the botty, admittedly, but this practice allows cool air to circulate the engine compartment while letting the heat from the exhaust manifolds out and away instead of gently cooking the carburettor while you're busily filling the tank...works every time!
In the event of vapour locking I've found that if you press the starter button and open throttle wide at the same time the engine will usually fire, (albeit in a pretty reluctant and doubtful way for a few seconds) and then it usually picks up.
Steve

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