Where exactly does the petrol go?

[Anonymous]

When you have to pump up the carb after the car sits for a while, where did the fuel go? I’ve been pondering this for 30 years! Evaporation? Out the intake manifold drain? Back to the fuel pump and/or tank? Where? Sometimes the float needle valve will stick on both of my cars when they’re cold, petrol won’t move, the lever does nothing, then a tap on the carb with a rubber hammer and the carb fills instantly. I don’t consider that a problem as such but where does it go when it goes? ❓

[Anonymous]

As the carburettor sits at the highest point on the engine the consensus is that it slowly drains back to the tank.

I have an inline non return valve between the carb and the fuel filter after the fuel pump, which does help, but still isn’t a 100% cure as the fuel still disappears eventually 🙂

[Anonymous]

But, the inlet to the carb is at the highest point on the carb. Anti-gravity petrol? It just doesn’t seem possible. It couldn’t maybe slowly drain into the cylinders, could it? But if it did that, it should drain out the line on the intake but it doesn’t do that since there’s no pool of petrol on the ground and if they did do that, wouldn’t Tractions be known for it? if I drive mine every day they start instantly with no pumping of the lever, more than a day of sitting, then I have to. The fuel can’t possibly evaporate that fast. I’ve been home recently recovering from surgery so I have time to ponder such an imponderable.

[Anonymous]

I am surprised to learn that anti-gravity petrol has not yet reached the colonies!

So what else is there? My first thought was possible syphonic draining of the carb fuel bowl – but I now realise that is not possible on two counts –
1) the fuel enters at the top of the bowl so, as soon as any is removed, the level drops creating an air gap between the remaining fuel and the inlet valve so the vacuum permitting the syphon will be lost, and
2) If the float valve is sticking in the closed position fuel cannot pass either way so the missing fuel cannot have left the carb via the inlet valve.

I don’t have the sticking float problem but, despite an in-line non-return valve and careful tightening of all pipe joints, I too suffer from having to prime the carb after much more than 24 hours standing. I can only think it has to be a combination of syphonic draining of the pipes and fuel pump plus evaporation from the carb – remember the volume of the bowl with the float in place is very small and, if the engine is hot when it is switched off, evaporation is almost certainly going to be enhanced.

Noah

[Anonymous]

The Solex 32 PBIC was used on various other cars such as French-built Hotchkiss-Willys Jeeps, early 60s Mercedes and many others. I wonder if they have the same trouble? I did own a 59 Mercedes 220S with two twin barrel Solex carbs and the fuel pump on that car had a priming lever as well. I recall only using it if the car sat for a week or more. It’s a puzzle, all right. Nope, no anti-gravity petrol yet!

[Anonymous]

I can’t help with suggestions but believe I’m having the same problem. I’ve just returned my car to the road and it was having a fuel problem when I tried to start it yesterday. I didn’t think to look for a priming lever. Is it obvious? And, how much priming is required typically?

Thanks

[Anonymous]

Lever should be obvious under the fuel pump and half a dozen strokes should see the fuel up to the carb

[Anonymous]

@OSL282 wrote:

Lever should be obvious under the fuel pump and half a dozen strokes should see the fuel up to the carb

Hmmm, I must have some non-standard fuel pump as there is no sign of any priming lever. One more thing to add to my list.

[Anonymous]

Do you have the modern replacement pump? Black plastic upper part and nozzles and metal lower part and no way to take it apart? That kind has no lever and the fuel disappearance problem is still there which will sure shorten the life of your battery with all the cranking. Throw that piece of rubbish away and get an AC type U fuel pump. It’s used on Triumph TR-250s and TR-6s. Obsolete Automotive in Port Edward, Ontario has them brand new for less than $80.00 (as of last year.) 1-800-265-7437. I have rebuilt type U pumps on both of mine and they’re better than the French pumps such as the Guiout. I still have the fuel going away but batteries last a long time.
As an aside, I rebuilt one of the pumps with an old, non-ethanol friendly kit. Didn’t last long but new kits will work with that watery crap.

[Anonymous]

There are different fuel pumps used on the Traction from S.E.V, Guiot plus the modern replacement you can buy from the Likes of Jose Fransen http://tinyurl.com/mrkcgct (as per the image below) which my car was fitted with when I bought it.

It depends if your trying to keep the car original looking or want more reliability 😉

[Anonymous]

Apparently I have the type that Larry describes. I’ll definitely replace it since it isn’t practical for me to use the car every day. Thanks for the suggestion, and great name for a parts company, i.e. Obsolete Automotive.

Meanwhile, is there a port on the carb that can be used to prime with an eyedropper or the like?

[Anonymous]

On my 1955 Familiale there is no priming lever. The fuel pump is an AC and the carb is a Zenith Stromberg 32 INA. I think these are both original and were fitted to late 55 production on the 11D engine? The previous owner fitted a rubber marine type primer on the fuel line. It all seems to work well and the car starts easily after a couple of pumps. Might be easier than replacing things if everything else works OK? Peter

[Anonymous]

Not sure how long that would last here in the EU with ‘ordinary’ fuel now going to 10% bio which is why I run the car on ‘Premium’ which has very little Bio content yet.

Running an older car isn’t that straightforward, is it 😕

[Anonymous]

I am led to believe the hand primer has been on there since 2008 so seems to be lasting. Not sure about differences in petrol quality between UK and Canada but I too use the “premium”grade.

[Anonymous]

I should have mentioned the new pumps that CTA and Jose Franssen sells, friends of mine have them and they work well and look good. One guy had a problem with his 11B with the shift rods hitting it, but he was able to adjust them slightly. They fit perfectly on a 15/6. No, there is no way to prime the carb with an eyedropper and pouring petrol down the throat is not a good idea. I’ve heard that the outboard motor type bulb works well too.
I’ve always thought that original SEV and Guiot pumps were made of cheap pot metal, likely wartime scrap that was melted down. I’ve seen these pumps warp where the diaphragm is located and fuel was pissing out. Also, on the Guiot you can’t replace the valves. Don’t know about the SEV.

[Author]

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