petrol return pipe ?

[Mickey taker]

Do I need to keep the primer bulb ?

I always thought they were for diesels .
I was going to just connect the fuel filter where the primer pump is and then run a length of pipe to the manual pump

[BX Meteor]

I haven't looked closely at the fuel lines in my engine bay for aaaaaaages.

I was surprised to see (I had completely forgotten) that my car is fitted with an anti-gassing device.

Everything in the pictures is original, except for the inline fuel filter which I renewed ages ago (I've had the car since 2004).

The routing for yours should be the same, except if you don't have an anti-gassing thing, the output from the inline fuel filter would go direct to the carb, and the return pipe for the tank would attach to the outlet above the inlet on the carb. However, like mine, the outlet is missing on yours, so if you don't have an anti-gassing thing maybe there was one once.

As for the question about the primer, I've just looked in your blog and it's only there to prime the pump. Take that to the forest with the pump and scarifice them together (but not until you know that the mechanical pump works of course ... I hope it does).

[Willy]

Building what on Brian said, my 1.6 has some internal leak somewhere causing all the fuel to drain out of the system back into the tank overnight, and the float bowl evaporates very quickly too.

Solution:

Keep the mechanical pump. They're only about £15 on the 'bay. Between the mech pump and the fuel tank (mounted on the fireboard) an electric pump is mounted, wired to a small switch mounted under the dash. A few seconds on this after the car's been stood for a week bleeds the system. Starting is still harsh, but once started the mech pump does all the work and driving for me has been problem free.

Hope that helps?

Edit - here's a photo of my leccy pump:



The garden hose feeds to the mech pump, and the piping thereon is OEM. See through piping is handy as you can see whether or not it's bled.

[BX Meteor]

my 1.6 has some internal leak somewhere causing all the fuel to drain out of the system back into the tank overnight, and the float bowl evaporates very quickly too.

Some good advice there, but in my experience I've never needed an electric pump.

If my car has been standing for some time, I make sure that the suspension is set to low (so that the starter motor is not wasting power on the hp pump trying to pump up the suspension as well), then just run it on the starter for about 20 secs (if you've got a good pump and float chamber, that's all it needs to fill the float chamber from dry).

I don't see how fuel from the float chamber can get back to the tank though, it's not possible. I also doubt if you have "an internal leak" (??) because if you did, your MPG would be like an F1 car (and as I say, there is no way for the fuel to get back from the float chamber, unless the float is stuck down, and even then IMO the fuel will spill over into the venturi because the return feed is higher as it runs over the top of the engine).

If you don't have fuel in your float chamber, it's evaporated, and nothing will stop that. IMO and in my experience, an electric pump is not required for daily use, and I can start my car in 30 seconds even if its been standing for several weeks.

EDIT: if you look at the routing in my car, there is no return to the tank directly from the carb, so any fault in the float chamber will cause fuel overflow in the carb. Hence, logically, if the original return from the carb was there as an "emergcy" over flow return, they would not have "improved" the car to the arrangement in my car. Thus the return feed to the tank is only an emissions requirement, nothing else. If one's MPG is bad, check the float level and the mixture setting, and same goes if one has trouble starting. Treat the disease, not the symptom. IMO an electric pump is treating the symptom

[BX Meteor]

Turns out I've only got 1 spare carb (and a spare auto-choke control), no idea where the other carb went

Anyway, as can be seen from the pic, the spare carb also only has the inlet, so the scrapyard car I took it from must have had a de-gassing thing as well.



Name on my de-gassing thing is Sofabex, which is also the name on the pump body.

Sofabex list pumps on their website, but nothing else, and I presume that degass is a painter in France

[Willy]

The fuel is evaporating from the float chamber naturally yes, the "internal leak" I'm imagining is just an airleak somewhere meaning that the petrol all drains back to the tank overnight through either pipe. Don't know why, but it does. There's no fuel in the pipes after standing for a day or two. The primer pump is solely to save caning the starter/battery like this every time I go out as I only really need to drive weekly at best, so it ends up standing alot.

Returning to Mick's car. I may sound naive/dumb here, but I thought that the fuel pump in a carby car solely moves fuel up from the tank to the float chamber at a fixed rate, or at least proportional to engine speed in a mech pump. When the float chamber says "I'm full, closing now", any excess fuel is free to return down the return pipe to the tank. Am I missing something? That's why I was puzzled to why Mick's leccy pump would make any difference - all it is doing is proving fuel at Xl/min just the same as any mech pump would. Hmm

[BX Meteor]

The fuel is evaporating from the float chamber naturally yes, the "internal leak" I'm imagining is just an airleak somewhere meaning that the petrol all drains back to the tank overnight through either pipe. Don't know why, but it does. There's no fuel in the pipes after standing for a day or two. The primer pump is solely to save caning the starter/battery like this every time I go out as I only really need to drive weekly at best, so it ends up standing alot.

Returning to Mick's car. I may sound naive/dumb here, but I thought that the fuel pump in a carby car solely moves fuel up from the tank to the float chamber at a fixed rate, or at least proportional to engine speed in a mech pump. When the float chamber says "I'm full, closing now", any excess fuel is free to return down the return pipe to the tank. Am I missing something? That's why I was puzzled to why Mick's leccy pump would make any difference - all it is doing is proving fuel at Xl/min just the same as any mech pump would. Hmm

Crikey, I don't know where to begin, there's a lot there that is mis-understood ..... and, in your youtube clip that battery sounds on its way out, the best thing you can do with a battery to prolong its life is take it out of the car occasionally and leave it on trickle charge overnight. I'll do a youtube of my car tomorrw, it's been standing a while now (with battery out).

OK
"I'm imagining is just an airleak somewhere meaning that the petrol all drains back to the tank overnight through either pipe. Don't know why, but it does" .... if you're imagining an airleak somewhere, I don't want to be rude, but you're imagining everything in that sentence

"I thought that the fuel pump in a carby car solely moves fuel up from the tank to the float chamber at a fixed rate, or at least proportional to engine speed in a mech pump. When the float chamber says "I'm full, closing now", any excess fuel is free to return down the return pipe to the tank. Am I missing something?" ..... take the top off a toilet cystern and you''ll get what is going on in a carb. The fuel pump provides fuel at pressure, just like the water main provides water at pressure. It doesn't matter whether the fuel is a lumpy stream, or a continual stream, it is still at pressure (try running a carb with gravity feed from a can, then watch the feed coming out of the mechanical pump at different engine revs, then put your finger over the end and see if you can spray fuel all over your garage like you would with a garden hose ).

There is not excess fuel, just as there is no "excess water" in your house to route back to wherever it's coming from.

The float chamber is there to give a tiny "pressure" to the jet(s), so that as the air runs past the jet(s) it is drawn into the air stream by venturi effect. If you want to watch the venturi effect, got to a shower, turn it on, and watch the shower curtain get drawn slightly towards the air-stream of water droplets. In this case, atmospheric pressure is involved in pushing the curtain towards the air-stream of droplets running close to it. Fluids and gasses are somewhat intercnahgeable in the venturi effect. In the carb, the fuel is sitting at the top of the jet, with not enough pressure to push it out, but when the air rushes by, the venturi effect draws it out and it gets mixed into the air stream.

The rate at which fuel is being drawn into the airstream from the jet(s) will lower the float chamber at that rate, as you imply. But in fact the needle valve will then be just open enough to let the same stream in from the higher pressure side (and as I imply in my example, even at idle from a "lumpy" mechanical pump, a closed valve then makes the fuel pressurised on the supply side). If you took the top off toilet cystern, and bent the arm of the float upwards so that the custern now fills to the overflow, then listen to the valve in the cystern, and you will hear what I am on about. There is no fuel flowing back to the tank in this car, and there never should be. If the car is driving on a flat level surface, then the fuel in the float chamber will be flat and level too, the float valve is not a "flip-flop" (on/off) valve, it is a linear valve that gets a small flow into the chamber from a pressurised tube.

Hope this helps

[Willy]

Well I understand perfectly well about venturi effects, throttles etc and how the fuel is drawn into the stream, my hypothesis was that the float chamber maintains a specified small amount of fuel ready to be evacuated through the jet, and its level is maintained by the float opening proportionately a valve which allows fuel in. Here is where I think I am getting lost.

In my mind, it works like this:

Scenario 1: Car idling. Very little fuel being sucked into the airstream, float chamber maintains a high level, keeping the needle valve practically closed, 95% of fuel supplied by the pump is bypassed straight to the return pipe back to the tank.

Scenario 2: throttle 100% open. Lots of fuel being sucked into the airstream, float chamber has a lower level thus opening the needle valve fully, allowing requisite more fuel into the chamber. Maybe only 20% of the fuel supplied by the pump is bypasses the needle valve and is sent back down the return pipe.

Vis a vie, hence why I see no reason why an electric or mechanical pump would make any difference, assuming they can both exceed the maximum fuel demand required an 100% throttle and are smooth in delivery (positive displacement or whatever). Okay, now you can pick holes and say where I am wrong

RE my "air leak", again my analogous explanation is as follows:

Bleed a hosepipe with water, and stick both ends in a bucked of water, water remains in hosepipe and water pistol starts first time, hooray. Put a pin prick in the top of the hosepipe, air gets in, the water all drains out and water pistol takes lots of pumping to bleed the system with water again.

Car/street stinks of petrol vapour whenever I park up.

edit I can tell that most of my petrol goes straight from the pump back down the return pipe, as when I look under the bonnet whilst idling, the petrol goes through the transparent hose at such a rate of knots it'd empty the tank in minutes if that was going straight to the engine.

[BX Meteor]

Well I understand perfectly well about venturi effects, throttles etc and how the fuel is drawn into the stream, my hypothesis was that the float chamber maintains a specified small amount of fuel ready to be evacuated through the jet, and its level is maintained by the float opening proportionately a valve which allows fuel in. Here is where I think I am getting lost.

In my mind, it works like this:

Scenario 1: Car idling. Very little fuel being sucked into the airstream, float chamber maintains a high level, keeping the needle valve practically closed, 95% of fuel supplied by the pump is bypassed straight to the return pipe back to the tank.

Scenario 2: throttle 100% open. Lots of fuel being sucked into the airstream, float chamber has a lower level thus opening the needle valve fully, allowing requisite more fuel into the chamber. Maybe only 20% of the fuel supplied by the pump is bypasses the needle valve and is sent back down the return pipe.

Vis a vie, hence why I see no reason why an electric or mechanical pump would make any difference, assuming they can both exceed the maximum fuel demand required an 100% throttle and are smooth in delivery (positive displacement or whatever). Okay, now you can pick holes and say where I am wrong

RE my "air leak", again my analogous explanation is as follows:

Bleed a hosepipe with water, and stick both ends in a bucked of water, water remains in hosepipe and water pistol starts first time, hooray. Put a pin prick in the top of the hosepipe, air gets in, the water all drains out and water pistol takes lots of pumping to bleed the system with water again.

Car/street stinks of petrol vapour whenever I park up.

edit I can tell that most of my petrol goes straight from the pump back down the return pipe, as when I look under the bonnet whilst idling, the petrol goes through the transparent hose at such a rate of knots it'd empty the tank in minutes if that was going straight to the engine.

scenario 1: no, absolutely not

secnario 2: no, absolutely not

Float chamber is there to provide a small "pressure" to the jet(s). Why go to the trouble of measuring the float clearance if your scenarios are true ? Float chamber is always level when driving on level ground, whatever the car speed i.e. whatever the rate of fuel consumption.

I never said an electric pump doesn't help, just unnecessary if you take off the carb, clean it out, check the jets and the float needle valve, check the float clearance, check the gasket. Aslo check that the mechanical pump is pumping fuel ok. Also renew your inline fuel filter. Also check that you have the correct spark plugs (your car sounds dead rough in the youtube that you might have the wrong plugs), and check the plug gaps.

"Car/street stinks of petrol vapour whenever I park up"
....... you might be confusing the smell of carbon with the smell of petrol (seriously), meaning your engine is running dead rough. Or it's running so rich that the exhaust contains a lot of unburned hydrocarbons.

"I can tell that most of my petrol goes straight from the pump back down the return pipe, as when I look under the bonnet whilst idling, the petrol goes through the transparent hose at such a rate of knots it'd empty the tank in minutes if that was going straight to the engine"
.... you're running incredibly rich at idle, which is what I thought when I watched your youttube and have said above.

You're rich your carb needs a good service

EDIT: re the float chamber, look at it this way. If your scenario 2 is correct, why do you want the level of fuel to be lower in the float chamber when the throttle is 100% ?? You honestly misundertand the role of the float and needle valve. It is there to keep the fuel at a constant level in the float chamber. The fuel in the pipe that feeds the carb is at pressure, and the float and needle are a device to allow fuel into the chamber such that the fuel level in the chamber is always at the correct height. Take the top off the carb (have you ever done this ?) and adjust the float so that it is at a lower level, then try to drive the car. The fuel level is supposed to be constant, so that the jet(s) receive the same pressure from that constant level, all the time.

As I say, there is no harm in fitting an electirc pump, but it is unnecessary to do this, if the carb, plugs, and battery are well maintained. If you leave your car standing for a few days and you have trouble starting it and you fit an electric pump as a solution, you have treated the symptom, not the disease.

[Willy]

Sorry for one confusion, Youtube video isn't mine! It's same engine car etc but off some Dutch gentleman whose channel I like to poke around. It was to show what would happen if I didn't have the primer pump to pre-bleed the system.

Again I don't think I've been clear enough, what I said, or at least was trying to in my "scenarios" is quite analogous (in my mind at least!) with what wikipedia says on float bowls:

The correct fuel level in the bowl is maintained by means of a float controlling an inlet valve, in a manner very similar to that employed in a cistern (e.g. a toilet tank). As fuel is used up, the float drops, opening the inlet valve and admitting fuel. As the fuel level rises, the float rises and closes the inlet valve.

My point was more that if the fuel isn't going from the pump down the needle valve, it's going to be shooting back down the return pipe. I understand how the float bowl operates, and why it is there, just not how fuel is delivered to it.

I never said an electric pump doesn't help, just unnecessary if you take off the carb, clean it out, check the jets and the float needle valve, check the float clearance, check the gasket. Aslo check that the mechanical pump is pumping fuel ok. Also renew your inline fuel filter. Also check that you have the correct spark plugs (your car sounds dead rough in the youtube that you might have the wrong plugs), and check the plug gaps.

Je sais, Linegeist (previous owner) did all this - he for some reason swapped the Solex for a Weber, which is what I'm running now, and that is the reason the primer pump is there, I think he took it from a scrapheap, idle speed drops nicley when the engine's warmed up then steadily increases for the remainder of your journey (throttle not fully closing?) up to about 1500rpm.

Deffo petrol, smell emanates quite obviously from the bonnet, exhaust smells normal (I've had my nose up there far too many times than I'd have liked when I suspected the HG was duff). Ironically, I believe the carb was actually set to burn lean to pass the MOT...[/i]

[BX Meteor]

Sorry for one confusion, Youtube video isn't mine! It's same engine car etc but off some Dutch gentleman whose channel I like to poke around. It was to show what would happen if I didn't have the primer pump to pre-bleed the system.

Again I don't think I've been clear enough, what I said, or at least was trying to in my "scenarios" is quite analogous (in my mind at least!) with what wikipedia says on float bowls:

The correct fuel level in the bowl is maintained by means of a float controlling an inlet valve, in a manner very similar to that employed in a cistern (e.g. a toilet tank). As fuel is used up, the float drops, opening the inlet valve and admitting fuel. As the fuel level rises, the float rises and closes the inlet valve.

My point was more that if the fuel isn't going from the pump down the needle valve, it's going to be shooting back down the return pipe. I understand how the float bowl operates, and why it is there, just not how fuel is delivered to it.

I never said an electric pump doesn't help, just unnecessary if you take off the carb, clean it out, check the jets and the float needle valve, check the float clearance, check the gasket. Aslo check that the mechanical pump is pumping fuel ok. Also renew your inline fuel filter. Also check that you have the correct spark plugs (your car sounds dead rough in the youtube that you might have the wrong plugs), and check the plug gaps.

Je sais, Linegeist (previous owner) did all this - he for some reason swapped the Solex for a Weber, which is what I'm running now, and that is the reason the primer pump is there, I think he took it from a scrapheap, idle speed drops nicley when the engine's warmed up then steadily increases for the remainder of your journey (throttle not fully closing?) up to about 1500rpm.

Deffo petrol, smell emanates quite obviously from the bonnet, exhaust smells normal (I've had my nose up there far too many times than I'd have liked when I suspected the HG was duff). Ironically, I believe the carb was actually set to burn lean to pass the MOT...[/i]

OK, your interpretation of what Wikipedia says is not my interpetation of what Wikipedia says. "As fuel is used up, the float drops, opening the inlet valve and admitting fuel. As the fuel level rises, the float rises and closes the inlet valve" this will happen over millimeters of movement, and indeed Wki is not exaclty correct, because the needle valve is a linear device, so it does not operate in exactly that way. Take a carb apart and try to blow through the needle valve, and move the needle up and down, it's linear in operation. I don't mind wikipedia, but are you using it to understand something, or are you saying you understand, and using it as a reference to say I'm wrong??

And if your car is Linegeist's, I'll say this: I remember his ad, and he put something like "this is not to be considered an everyday car" and "I fitted a primer to fill the carb as I do not use the car all the time". I would say about my car "this is not to be considered an everyday car" and "this car is so well maintained, that even if left standing all the time, it still starts easily".

If you're going to give a youtube that is not your car, then please say so (I didn't think you were in the drivers seat, but I did wonder why it had dutch number plates). I would have spent a lot less time trying to say what is wrong with a car that is not yours

Finally, if the engine speed is rising after it has warmed up, then the carb needs adjusting properly (mixture, idle, auto-choke). If he set it lean, then he may have also raised the idle speed to cope when it is cold during the phaase when the autochoke starts to open.Alternatively, you may be right about the throttle sticking causing idle speed rising (but I'd like to see it for myself) , but I suspect that if it slowly rises to 1500 as the engine warms up, the idle is just too high (whether on the idle scew or the cable or somewhere). Trouble is, if you cure that, then it may cut out during the auto-choke closure phase, so the auto-choke needs adjusting too.

And if you really can smell fuel, then you should not be driving it. What is the MPG ??

I live in Loguborough, your location says Birmingham/York, is the car in Birmingham, which side (I would want to see it from cold).

EDIT: btw my MOT man adjusts my car to lean if it fails the hydrocarbon test (I've known him 25 years), then I adjust it back a few days later. Lean is not good, it could be running hot, I've often wondered whether to source slightly hotter plugs and keep it lean. And finally, if one wants to prime a carb with an empty float chamber and it has a mechanical pump ....then the best way is to keep a screwdriver, a small funnel, and a clear tube ready for the first time one starts it up. Undo the feed to the carb, fit the clear tube, put a funnel at the end of the tube, and pour in a bit of petrol until you see petrol at the bottom of the clear tube. Then remove the clear tube and put the feed back. I don't do that because I use the starter motor indstead. If one uses the BX frequently, this should not be necessary.

[Willy]

Again I appreciate that the needle float movement is minimal, my description was intended to be of an exagerrated account rather than say "in a very minor way" after everything. I've studied plenty of control systems to know how they work. And again sorry, I was not trying to reference that article to dispel what you were saying in anyway, just to try and substantiate that I understand. Sorry if there was confusion. Besides anyway this is faaaar detracting from the original point of how the fuel gets to the float bowl's needle valve in the first place. Originally, I was trying to explain how I thought that having a different type of pump would make no difference suffice that it can supply sufficient fuel to that valve.

Re the video, thought the Dutch numberplate was a clue! Again sorry for the confusion although that driver does look weirdly similar to me... My engine is quite a bit smoother/quieter than that and the car rises normally.

Re Bob's car, I don't use it every day, and if I had the necessity to, would sell. However, that is more out of wanting to save money on fuel (I drive very cautiously but only get about 45mpg) and don't want to waste a good car on tedious commuting.

I'm guessing that my idle-speed issue is the throttle sticking open. I'll turn it on, the autochoke sticks it up to about 2000, a few traffic lights later and it'll be at about 800. 20 or so minutes later and it'll be dropping down to about 1300. When I first bought the car it'd drop down to about 1100max, so I imagine a couple of thousand miles' driving has gunked it up a little more (cleaning is on the to-do list when I'm next at my parents up North and have garage facilities).

I imagined the fuel smell was evaporation from the float bowl. Once it's dried up, no smell. Currently at studies-home in Birmingham B29 (South), so the wrong direction

[BX Meteor]

Idle speed on my BX when fully warm is about 800 rpm, I'm not surprised you can see fuel running through the feed pipe on idle, you're probably using less petrol when you're driving (to be factual, your fuel useage will be far better when driving).

I've never stripped down the Weber carb, but I think it is similar to the Solex carb. There are 3 jets in the Solex carb: an idle jet, a jet for the first venturi, and a jet for the second venturi. The main problem on these carbs is the auto-choke, there are quite a few threads in this forum about the auto-choke. A lot of gauges are required to set up the auto-choke properly, only after that has been done can the idle speed and idle mixture screws be adjusted (and the ignition system should be perfect and the valve clearances too).

Best thing to do with any carb, is, don't be scared of it. Take it off the car, and then take off the top of the carb. There is a paper-type gasket between the two halves, this may have perished, which is why you might be smelling fuel if your MPG is OK. Take out all the jets (make sure you know which one goes back where, though they're usually not inrterchangeable). Remove the float and needle valve too. Familiarise yourself with where the idle speed screw is (and how it operates), and also the idle mixture screw, but don't adjust them.

Then clean up both halves as much as you can. Don't touch anything in the auto-choke on the side, as adjustments there require correct gauges to set it up.

Put it all back together carefully then put it back on the car, and sometimes just doing this much will improve it a bit. If the idle speed is still high when the engine is warm, check that the throttle cable is not tight, then adjust the idle speed screw (the mixture screw also affects idle speed but don't adjust that) to reduce the idle rpm. Then when starting the engine from cold, be aware that during the warm-up phase of the auto-choke, the idle rpm may go too low and the engine will cut out. If this is so, you need to check the water levels are definitely getting to the auto-choke properly, and if they are, the auto-choke may need adjusting. At the very least you need a Haynes for that.

[Way2go]

It seems that although you are both looking at the Cistern approach you are missing the benefit of having the return pipe.
Cisterns are usually attached to a water main or fed from a cold water storage tank in the loft. Mains fed have smaller nozzles in the ball valve so that the valve can be closed easily against the pressure whereas the tank fed ones have larger orifices. Generally it is quicker to replenish the cistern from the tank than the mains because of superior flow rate through the larger orifice.
Same for the carb float chamber. The inlet can have a larger orifice if the float does not have to battle against the inlet pressure. The return allows this as there is somewhere for excess pressure to go when the float valve closes. Being able to have a larger effective orifice in the float valve allows the mixture to still be correct at higher revs giving increased power and consequently not be running lean.
Hope this helps.

[BX Meteor]

/\ yeah it does,

I have a car from the 50's with an SU carb but no return to the tank.

On my BX, there is no return to the tank from the carb (see my pics), but there is a return from the "de-gassing" device (a Citroen specialist told me that was what it is, about 15 years ago, I actually assume it's not called that because I can't find anything about it). This device must be to ensure that the presssure feed to the carb is not too high, returning fuel to the tank but keeping a sufficent pressure up to the carb.

I'm not sure what arrangement Willy has on his car. I notice that in the Haynes manual there is a direct return from the carb, and I remember that from when we had an "E" reg 1.6 which we got rid of in 1998. But ever since then they have had this "de-gassing" device, which I totally forgot about until I took the pics.

I was talking about the pressure at the needle valve from this device, I think that might have been the confusion.