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Vapour locks
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Uncle Joe
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PostPosted: Fri Jul 25, 2008 3:12 pm    Post subject: Vapour locks Reply with quote

The subject of vapour locks came up in another topic a while ago. As I cant find this topic, I thought that I would restart it.

Several solutions to this problem turned up, but one was absent. Why not simply fit a vapour separator between the pump and carburettor? It only came to my mind as I am going to fit one shortly....

Could these separators be something new to most people on here?
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Roverron



Joined: 04 May 2008
Posts: 134
Location: Yorkshire

PostPosted: Fri Jul 25, 2008 6:32 pm    Post subject: Reply with quote

Never actually heard of them. When I got my Rover I was plagued by vapour locks. I tried everything anybody suggested until I somebody said to fit an electric petrol pump would be the way forward, and it solved my problem. (Except when it packed up one day halfway through some roadworks on a bridge Embarassed Strange I've never had trouble passing water before.)
The Rovers exported to hotter countries had an electric pump fitted as standard and modern fuels are more volatile than ones available years ago. Incidently in the first issue of Freewheel (The Rover Sports Register magazine) the first technical article was about vapourisation.
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Uncle Joe
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PostPosted: Fri Jul 25, 2008 7:04 pm    Post subject: Reply with quote

This is a photo of one that is similar to what I will be fitting.



It should be easier to fit than an electric pump simply because there is no need for electrical connections....
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Phil - Nottingham



Joined: 01 Jan 2008
Posts: 1252
Location: Nottingham

PostPosted: Fri Jul 25, 2008 10:18 pm    Post subject: Reply with quote

Never heard of them - vapor lock is quite common with older cars especially when their mecahnical pumps have worn and teh pressure drops. Modern unleaded is also more prone to this.

Where are these little devices sourced from - are they fitted near the pump or carb.

The transparent plastic fuel filters would seem to be the same - they do not prevet vapour lock though.

Electric pumps do resolve this effectively but are noisy and expensive
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Uncle Joe
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PostPosted: Sat Jul 26, 2008 9:10 am    Post subject: Reply with quote

The one pictured is a Chrysler reproduction part that fits on to the timimg cover. So its nearer the pump than the carb. There is a later version though that is a filter and fits closer to the carb. So I dont think positioning is critical.

Probably the easiest source is a VW dealer, I'm pretty certain that separators are fitted to Golf/Jettas, as well as various other common cars.
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Sat Jul 26, 2008 12:55 pm    Post subject: Reply with quote

My old Jag suffers from this if the engine is hot and I park it for a short time in hot weather.
When I come back to it the SU pump just rattles away but appears to achieve very little. I'm not sure I understand what's going on here. If the vapour was between pump and carbs I don't know why the pump fails to work so it must be between tank and pump.

The pump is mounted high on the bulhead so there is a vertical pipe of say 18" supplying the pump input.

Peter
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Uncle Joe
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PostPosted: Sat Jul 26, 2008 1:02 pm    Post subject: Reply with quote

Peter, there are two kinds of SU pumps, ''pushers'' and ''pullers.'' If you have a pusher mounted on the bulkhead, then this problem can occur, as it can if you have a puller mounted near the tank.
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Sat Jul 26, 2008 5:43 pm    Post subject: Reply with quote

Hi UJ,

I believe I have an LP type pump which is designed to pull but I still get vapourisation in hot weather. I suspect that if I were to insulate the input pipe then I might solve the problem. Perhaps I should carry a can of freezer spray just verify where the problem lies. Confused

Thanks,

Peter
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ukdave2002



Joined: 23 Nov 2007
Posts: 4100
Location: South Cheshire

PostPosted: Sun Jul 27, 2008 8:04 am    Post subject: Reply with quote

Related story published in this months Morris Register news letter, no idea if it is true, but is ammusing Very Happy

Quote:
THE CASE OF THE WRONG ICE CREAM!
For the engineers among us who understand that the obvious is not always the solution, and that the facts, no matter how implausible, are still the facts.

A complaint was received by the Pontiac Division at General Motors:
'This is the second time I have written you, and I don't blame you for not answering me, because I kind of sound crazy but it is a fact that we have a tradition in our family of ice-cream for dessert after dinner each night But the kind of ice-cream varies so, every night, after we've eaten, the whole family votes on which kind of ice-cream we should have and I drive down to the store to get it Its also a fact that I recently purchased a new Pontiac and since then my trips to the store have created a problem. You see, every time I buy vanilla ice-cream, when I start back from the store my car wont start If I get any other type of ice-cream, the car starts just fine. I want you to know I'm serious about this question, no matter how silly it sounds.
What is there about a Pontiac that makes it not start when I get vanilla ice-cream, and easy to start whenever I get any other kind?

The Pontiac president was understandably sceptical about the letter; but sent an engineer to check it out anyway. The latter was surprised to be greeted by a successful, obviously well-educated man in a fine neighbourhood. He has arranged to meet the man just after dinner time, so the two hopped into the car and drove to the ice-cream store. It was vanilla be-cream that night and, sure enough they came back to the car, it wouldn't start.

The engineer returned for three more nights. The first night, the man got chocolate. The car started. The second night, he got strawberry. The car started. The third night he ordered vanilla. The car failed to start
Now the engineer, being a logical man, refused to believe that this man's car was allergic to vanilla be-cream. He arranged, therefore, to continue it for as big as it took to solve the problem.

And toward this end he began to take notes: he jotted down all sorts of data, time of day, type of gas used, time to drive back and forth, etc.
In a short time, he had a clue: the man took less time buy vanilla than any other flavour. Why? The answer was in the layout of the stone. Vanilla, being the most popular flavour, was in a separate case at the front of the store for quick pickup. All the other flavours were kept in the back of the store at a different counter where it took considerably longer to find the flavour and get checked out.

Now the question for the engineer was why the car wouldn't start when it took less time. Once time became the problem - not the vanilla be-cream - the engineer quickly came up with the answer. vapour lock It was happening every night, but the extra time taken to get the other flavours allowed the engine to cool down sufficiently to start When the man got vanilla, the engine was still too hot for the vapour lock to dissipate.

Moral of the stay: even insane-looking problems are sometimes real.


Last edited by ukdave2002 on Sun Jul 27, 2008 8:17 am; edited 1 time in total
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Uncle Joe
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PostPosted: Sun Jul 27, 2008 9:38 am    Post subject: Reply with quote

UK, do you happen to know the different designations for the different types of SU pumps?
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Sun Jul 27, 2008 10:49 am    Post subject: Reply with quote

Hi UJ,

Here are the pump designations

http://www.gowerlee.dircon.co.uk/Pumps.html

Peter
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Kaybee



Joined: 27 Dec 2007
Posts: 147
Location: Croydon, Victoria, Australia

PostPosted: Sun Jul 27, 2008 1:33 pm    Post subject: Reply with quote

Hi Peter, your Jag problem is very similar to what happens with early Flathead Ford V8's in hot weather. They have a fairly small mechanical pump on the very top of the engine, where it gets nice n'hot and it's also about 20" above the height of the fuel tank. The original steel fuel line is 1/4" o.d., inside diameter is about 3/16". I discovered that it was quite hard to blow through the line even when empty , and figured that it might be the same for the poor old fuel pump. So...I replaced the steel line with modern rubber fuel hose of 5/16" i.d.....and that was the end of the problem, even in 40 degree weather. Maybe it was because the resistance to flow was decreased, or perhaps the insulating effect of the rubber hose had something to do with it, but whichever, it fixed it ! Smile
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Sun Jul 27, 2008 6:58 pm    Post subject: Reply with quote

Thanks KayBee, I suspect it is the insulating properties given that the pump works in cooler conditions. When the fuel is flowing it will cool the pipe but when you stop the metal pipe will transfer more heat to the now static fuel than would the rubber one.

Peter
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Greg



Joined: 03 Dec 2007
Posts: 445
Location: Dreamland Margate

PostPosted: Sun Jul 27, 2008 10:20 pm    Post subject: Reply with quote

Vapour lock is sometimes a problem on the old Ford Sidevalves, although some do suffer from it and others,(fortunately like myself), don't.
Over the years reading about different remedies for the problem, the most common way to cure it seems to be the fitment of a 'Heatguard' between the fuel pump and the exhaust manifold, being as they are very close together. A chap told me just today at a show that his old Ford Pop had this problem and that he bought the above from a Ford dealer themselves.
Don't know if this is of any help?
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peter scott



Joined: 18 Dec 2007
Posts: 7113
Location: Edinburgh

PostPosted: Mon Jul 28, 2008 1:45 pm    Post subject: Reply with quote

The carbs, pump and fuel line are all on the near side of the car and the exhaust manifolds are on the off side. Having said that, there are two independent exhaust systems, one for the front three cylinders and the other for the rear ones and one of them has a dog leg in it so that it passes under the gearbox and across to the near side of the car. There may be heat rising from the near side pipe in addition to general engine heat.

I don't think it's a radiation issue as the fuel line runs along the outside of the chassis whereas the near side exhaust runs between transmission and chassis rail.

If I can find an acceptable looking insulation material then I think I might try lagging that part of the fuel line where it rises up the bulkhead. Mind you, weather being as it is here in Scotland this is not a frequent problem. Wink

Peter
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