MGB Persistent fuel leak

[skiday]

HI folks.

My MGB (1971) 1800 is suffering (or rather I am suffering) a persistent fuel leak. In the past I had the occasional overflow from the float chambers, but recently it became persistent. It was either weeing out either from the fuel pump area or one or both of the overflows. I cleaned and checked the pipe connections to the pump and cleaned the float chamber needles and seats but to no avail. To me it seemed as if the pump was not regulating itself and putting out too much pressure. But both my mechanical chap and MGOC tech dept said that wasn't likely and that I should replace the pump output flexi and the needles and seats, which I did (btw, I notice that the needle tips are now rubber instead of brass - I can't think that they will last as long, especially with ethanol in the petrol attacking them), but although the pump area now seems to be OK the fuel is still pouring out of one (either) or both of the float chambers (about a yoghurt pot per minute). I tried it around the block and it was very rough. I tried clamping off the tube off the overflow and, of course, it flooded the chambers. According the spec for the year this car would originally have had a pump with parallel in and out, but mine has obviously had a replacement as the in and out are at 45deg. It makes a hell of a clicking noise as it works which you can clearly hear whilst driving. According to MGOC these are very reliable units that do lot get more powerful with age, but that's the only explanation I can come up with, as given enough pressure the float chamber needles will always be overcome. Does anyone have any other ideas? And if it is the pump that needs replacing, which type should I go for? If I spend itro 100 for a pump and it doesn't cure it I'll be well cheesed off!

Thanks for any replies chaps

Andrew

[nta16]

the pump is reacting to its demand, very probably not the pump unless they sent you a high pressure pump by mistake

don't believe everything you read and hear about ethanol especially from old fart classic owners that very rarely ever drive their cars (if that includes you put the cap on)

you would have got Vitron needles, you'd have to confirm with the suppliers and SU but I can't see they'd sell them if you can't use them with the fuel generally available today (which is very low ethanol anyway)

you need to check your fuel bowls are clean of crud, rubber and grit - any rubber suspect the any rubber fuel hose especially if you've installed it in the last few years - my advice, from more than one experience, is if you need to replace any rubber fuel hoses don't use the 1/4" stuff use modern, 6mm I found fits better than 1/4" too, I used, from Halfords, G4509 Goodyear Fuel/Emission - DIN 73379-1 - 6.0 mm X 3 mm - 2B >NBR/PET/CSM<

you could also check the condition of the floats and that the float levels are set correctly and that you've installed the needle and seats correctly see bottom vid

note what's on this John Twist video - Needle and seat - http://www.youtube.com/watch?v=pVX_JClyeDQ&lis...

Setting the Float Height - http://www.youtube.com/watch?v=82YNx-RkGNI&lis...

Edited by nta16 on Monday 26th May 15:42

[v8250]

OP, much of what Nigel has written above is correct but there are a few other points to help.

Firstly, ditch your SU pump - they're crap and cause more problems than most owners will ever admit. Fit a blue top Facet pump with a large fuel filter between the the tank and the pump input...replacing all flexible hoses with modern ethanol ready fuel lines. Whilst doing this it's worth checking the condition of the main steel/cupronickel fuel line and give it a blast through. Then, fit Filter King glass bowl filter in engine bay before the carbs - this has an adjustable fuel flow regulator on top...set this up to specified peak fuel flow output plus a bit. Then remove carbs, inspect and set up float chambers, clean carbs meticulously. Contact Burlen Fuels in Salisbury and order a new set of needle without the rubberized ends. Here are some picks to show where to install. Once complete you will have no fuel problems.

[Geordie MGmike]

All good advice above.
I suspect very fine rust particles from the tank and it doesn't take many to keep a float valve open!

I've never had a problem with well maintained SU pumps and, unlike V8250, don't see the need for all that effort on a standard car (I might on a 1950 or 2100). I do agree with fitting copper fuel pipes in place of the original steel and electronic's in place of the old points in the pump is worthwhile but there again, I am a trained electronics engineering so I would

As a quick fix try a cheap plastic fuel filter between the fuel pipe and the carbs. Worked a treat for me and after running a few tanks of petrol through I was able to discard even that.

Best of.....

[nta16]

you're making an assumption that Andrew has a SU fitted now (or missed the fact that its new) possibly it might be the overpriced SU points type or overpriced SU electronics type

(having had a long spell of agreeing with v8250) - I disagree that there's a need to change the pump and certainly to a Facet, other can be just as good if not better and a lot less noisy than some of the Facet designs

on a standard or even reasonably tuned B there's no need for a fuel regulator (even probably on a 1950 or 2100)

from the SU web site - The most popular had a brass body with a spring loaded, stainless steel tip, mounted in a nylon needle and would withstand a pump pressure of about 6psi. Now are all fitted with a VITON tip.http://sucarb.co.uk/technical-carburetter-maintena...

Geordie MGmike said:

As a quick fix try a cheap plastic fuel filter between the fuel pipe and the carbs.

I forgot about that but I'd say have them permanently fitted and replace at each annual service, they're less than a couple of quid so why take a chance

[jagracer]

There's nothing the matter with the SU pump that a new set of points wont cure and it will stop clicking when it gets full pressure from the carbs. Your problem will be incorrect needle seating (doubtful), st in the needle, floats set too high or the floats are leaky and sinking.

[wildoliver]

Nothing wrong with su pumps at all, most people who Witter about them being u reliable don't take in to account the fact that many are well over 20 years old when they start giving issues. I've had rubber bumper cars that appeared to be on their original pumps. Hardly unreliable. A bad su pump is a pain but so is any bad fuel pump, at least su pumps rarely go inop without warning they can go on for months if not years needing the "tap" to make them start up.

Anyway this fault is clearly the float valves not cutting off the fuel, nowt to do with pumps or any other outlandish explanation, either the valves aren't closing because they ate A: crap or B: dirty. Or the float isn't floating or is sticking on the shaft or possibly is badly set. It's a 5 minute job to do I'm sure there is a how to on YouTube somewhere.

[skiday]

I appreciate the time take to reply to my problem, but I have to confess I'm still not clear what to do next because;

The system was working before so therefore it should be possible to get it working again without adding an adjustable fuel flow regulator/filter or different pipe work, although I'm happy to add a cheep little fuel filter. Something in the existing system is wrong and that is what needs repairing or replacing.

The punp is not the original type, but was on the car when I bought it. I had it out briefly, but did not identify it, but it does have a blue top (but I don't know if that makes it a 'Facet' pump)

If the new Vitron tipped needles don't work then why do they make and sell them? (bought from MGOC)

The vid for setting the float height was for the older style carb with a metal fork being lifted by the float, but mine are the simple all in one plastic float which moves the needle itself as seems not to need setting at all and would appear to be working correctly. I have tested them and when blowing with all my might I can't blow past the needles.

I have cleaned out the needles, seats, & bowels and they are as clean as a whistle.

I will go and have another try now to see what I can do bearing in mind all the above advice.

Thanks

Andrew

[wildoliver]

While I stand by my above post when you pull a fuel pipe off the car can you keep your thumb over the end of the pipe or does fuel spray all over the place? I suggest this as you say its not the original pump so it could be anything, my advice isn't hugely health and safety friendly by the way but use your common sense. A b fuel pump feeding carbs doesn't need to be hugely powerful, I do wonder if someone has fitted a facet pump without reg. What does the pump look like? The su pump is a very identifiable item there are a number of very similar design aftermarket pumps which are also fine, if however it looks like a round can or square block then its an aftermarket pump like a facet which probably flows far more fuel than desired. Take a picture and post it up. If it is an su type pump though it will be your float chambers that aren't working properly.

[nta16]

as always a good quality photo (with the subject in focus) would help

I think this blue top on the pump *might* be a red herring as my pump has a blue top but is a Q&H alternative pump, nothing like a Facet -



again the video of setting the float height was to show the principle, the vid showed a lid from a T-type which was an earlier model to the B

a couple of questions that come to my mind are, have you fitted any other parts recently and what debris did you clean out from the bowls and needles??

[Geordie MGmike]

skiday said:

I appreciate the time take to reply to my problem,

No problem, part of our reason for being here is to help

skiday said:

but I have to confess I'm still not clear what to do next because;

I know this is going to be difficult but forget what you've done so far and start again in a structured way with the guidance given here.

skiday said:

The system was working before so therefore it should be possible to get it working again without adding an adjustable fuel flow regulator/filter or different pipe work, although I'm happy to add a cheep little fuel filter. Something in the existing system is wrong and that is what needs repairing or replacing.

Agreed, but finding the cause may need the addition of a filter to catch very small particles of rust you can't see but will hold a valve open.

skiday said:

The punp is not the original type, but was on the car when I bought it. I had it out briefly, but did not identify it, but it does have a blue top (but I don't know if that makes it a 'Facet' pump)

As Nigel, a picture would help next time you take it off, but for now we'll assume it worked find before and will be fine in future until you prove it's faulty!

skiday said:

If the new Vitron tipped needles don't work then why do they make and sell them? (bought from MGOC)

I'm sure they do work but a lot of people like the solid version as they are believed to last longer.

skiday said:

The vid for setting the float height was for the older style carb with a metal fork being lifted by the float, but mine are the simple all in one plastic float which moves the needle itself as seems not to need setting at all and would appear to be working correctly. I have tested them and when blowing with all my might I can't blow past the needles.

As long as they are not punctured and taking in fuel you should be okay here. Also remeber that the pump pressure is only a few pounds and way less than you pushing on the float to hold the valve closed. The valve should have a spring loading which you should not exceed when testing the valve.

skiday said:

I have cleaned out the needles, seats, & bowels and they are as clean as a whistle.

Great, now add a cheap filter in the fuel line just before the first carb. You'll be surprised how small a rust particle can cause you problems (much smaller than a grain of sand).

skiday said:

I will go and have another try now to see what I can do bearing in mind all the above advice.

First thing to try is the see if the pump stops running when the system is pressurised. Either pull the pipe at the carb and stick your finger over the open end or clamp the hose to close it off. If the pump stops and there are no leaks elsewhere you are half way there
Clean the float valves again (with compressed air if you can get it), add a fuel filter and you should be sorted.

Best of...

MGmike

[skiday]

Well I have a photo from before I changed the flexipipe. It's now back in situ so I'd prefer not to remove it again to photograph it. When I cleaned the overflow bowles and needles I didn't notice any dirt or debris in there, but I cleaned them anyway.


MGmike - Small note; when I tested the floats I didn't push them up manually, I floated them (one at a time) in a cup of water to ensure they were only pushing up with their own ability to float and then blew through a short bit of tube added to the inlet pipe.

Edited by skiday on Tuesday 27th May 16:43

[nta16]

sorry that I didn't make it clear but I for one wouldn't suggest removing the pump, I meant a photo of the pump in situ

and well that photo is interesting, the over elaborate fittings and soldering of solid pipe suggest the previous owner might have been a fan of industrial plumbing - and using adjustable pliers instead of fixed sized spanners or perhaps some fittings are reclaims

good thing you replaced the flexi-pipe as the braid can hide deterioration of the rubber hose below

usually both the inlet and outlet of the pump are on flexible hoses

perhaps some might know or recognise the DB6M casting to the top and be able to recognise the pump

as you say the pump worked OK before then possibly it should work OK again

[Geordie MGmike]

skiday said:

Well I have a photo from before I changed the flexipipe. It's now back in situ so I'd prefer not to remove it again to photograph it.

Hmm I don't recognise the pump model but it's defo not standard

skiday said:

When I cleaned the overflow bowles and needles I didn't notice any dirt or debris in there, but I cleaned them anyway.

As said previously, you might/will not see a particle of the size needed to cause problems...

skiday said:

MGmike - Small note; when I tested the floats I didn't push them up manually, I floated them (one at a time) in a cup of water to ensure they were only pushing up with their own ability to float and then blew through a short bit of tube added to the inlet pipe.

Good man, why didn't I think of that!

Ok there are still a couple of possibilities.
1, Crud, fit a cheap filter to eliminate
2, The pump pressure is too high for the spring loading in the float valves. Refit the old valves as a quick check or get a low pressure gauge to measure the actual pressure (should be around 3-5 psi). Or replace the pump or fit a regulator/filter!

Best of...

MGmike

[jagracer]

It looks like a butchered Morris Minor pump so it should be fine.

[skiday]

I've just come in from trying again. The left/foremost carb was overflowing with ing. on. I disconnected the fuel supply pipes at the carbs, blocked them off and turned on the ing. - no leak at the pump or any other area. I cleaned the needle and seat, inspected the float as it occurred to me that the float might wear where it touches the needle, but it is as new. Reconnected, ing. on - pump clicks a few times and stops completely - no overflow. I started the engine and it was VERY rough, as if on only 2 or 3 cylinders - however - no overflow. Left to idle for a few minutes, but it didn't improve - it was even backfiring. On switch-off and then putting ing. back on I got a very slow tick from the pump but no overflow, which as there was no leak anywhere can only mean it was now slowly pumping into the cylinders.

I have ordered an in-line fuel filter, but there is no obvious place to fit it as there is a hard pipe from the pump to the engine bay, then the braided flexi-pipe goes to the carbs. Where would you recommend?

[wildoliver]

Is it just me or is that float chamber at an angle?

[Geordie MGmike]

wildoliver said:

Is it just me or is that float chamber at an angle?

Might be just the picture or you as the fuel in the bowl looks to be settling level.

[Geordie MGmike]

skiday said:

I've just come in from trying again. The left/foremost carb was overflowing with ing. on. I disconnected the fuel supply pipes at the carbs, blocked them off and turned on the ing. - no leak at the pump or any other area. I cleaned the needle and seat, inspected the float as it occurred to me that the float might wear where it touches the needle, but it is as new. Reconnected, ing. on - pump clicks a few times and stops completely - no overflow. I started the engine and it was VERY rough, as if on only 2 or 3 cylinders - however - no overflow. Left to idle for a few minutes, but it didn't improve - it was even backfiring. On switch-off and then putting ing. back on I got a very slow tick from the pump but no overflow, which as there was no leak anywhere can only mean it was now slowly pumping into the cylinders.

Yep, I've had that one too. What's happening is the valve is working but needs a little more spring pressure to close fully. By doing so it lifts the fuel level in the float bowl and also the main jet. In this instance the fuel level is at the point where the fuel runs out of the main jet into the inlet manifold but the valve closes sufficiently to prevent an overflow. If you take the dashpot off you'll see the fuel pulsing out of the jet in time with the click of the pump. As a result the car is running very rich on that carb and this causes the rough running.

I'm still going with crud and a filter should cure it..... But, I'll hedge my bets and consider a faulty valve
Make sure the viton ring has no damage, pitting etc and try again.

skiday said:

I have ordered an in-line fuel filter, but there is no obvious place to fit it as there is a hard pipe from the pump to the engine bay, then the braided flexi-pipe goes to the carbs. Where would you recommend?

Remove the flexi from the Tee and this goes into the filter. You'll need another flexi from the outlet of the filter back to the Tee.

Best of.....

MGmike

Edited by Geordie MGmike on Tuesday 27th May 19:47

Edited by Geordie MGmike on Tuesday 27th May 19:48

[nta16]

if you need more room or want to make a neater job of installing a filter you could perhaps change the float bowl caps around so the you feed the front carb first thus giving you a long length supply to cut into for the filter