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MG MGB Technical - Fuel Leak

I am quite new to MG's

My 1977 MGB GT appears to have developed a small leak - from about the dead centre of the car - and it appears to be petrol.

When the engine is running the drip appears about once a second. Help!
Chris

The fuel line runs down the driver's side of the transmission tunnel - could be a leak from the pipe or from the hose at the rear end, the fuel running along the pipe.

You need to crawl under and have a good look - but don't strike a match!!
Chris Betson

Hi..

The favourite place for a fuel leak is from the tank, the top of which is rather prone to rusting.

The leaking fuel might be making it's way to the centre of the car before dripping off... do you park on a downward slope ?.

Don
Don

Chris. When the engine is running, or the ignition switch is in the "run" position, power is supplied to the fuel pump, located at the rear of the car, right hand side, sticking into the boot/trunk. When power is supplied to the fuel pump, it will click until it pressurizes the fuel system, then will only click (operate) again when the system pressure drops. This is for the original SU pumps.

The first thing to do is get the car up on jack stands or a lift, then clean the fuel lines from the tank to the pump and the pump forward, as best you can. Turn on the ignition switch and pressurize the system, then see if you can find where the drip is coming from. The rubber hoses from the fuel tank to the fuel pump and the fuel pump to the metal "hard line" are common leak areas. The fuel pump itself is fairly rare, but has been known to leak. The hard lines can crack either through rusting, rubbing or fatigue and should be inspected. Bit of of bear to inspect the hard lines as it is bundled with the wiring harness lines going backwards and the battery cable going forwards. You will also have a fuel tank vent line going from the fuel tank to the charcoal cannister on North American models. Do not know if the UK had adopted the charcoal canister by that time. If so, you also need to check the line from the fuel tank to the charcoal cannister as it, too, can contain fuel. Les
Les Bengtson

I have cleaned the underneath of the car - the leak does not appear to be coming from a pipe but wells up in a bubble under the centre fream (than crosses the car) and then drips

Any more thoughts??
Chris

Chris. Not sure exactly where the "centre fream" is. Is this the crossmember that supports the rear of the tranny or the cross brace ahead of the tranny crossmember? In any event, petrol/gasoline can only come from a single source--the fuel tank. After that, it follows a well defined trail up to the fuel pump, then from the fuel pump forward to the engine compartment. The second, far less probable source is the vent line running from the charcoal canister back to the fuel tank vent and vapor seperator. Both of these hard lines run along side each other, along with the main battery cable and the wiring harness to the rear. If you have dripping, you need to unbolt the wiring harness, cable and hard lines, seperate everything out and find where the leak is coming from. Les
Les Bengtson

Les,

We don't have charcoal canisters or vapour separators on UK cars.


Chris,

Has to be the fuel line which goes the length of the car - check it where it goes past the x member.
Chris Betson

Chris. Thank you. Once again you have initiated those of us in the US into the mysteries of the UK cars. Most of us are aware that, at some point, the UK cars got cats. Paul Hunt has mentioned this in passing. However, we are not fully aware of exactly what bits and pieces were picked up over the years for the UK and export (other than NA) cars. The charcoal cannister and fuel tank vented to the cannister are relativly benign forms of emissions controls which do a minor amount of good and, to the best of my knowledge, nothing bad. Hence, my presumption that the UK cars had this feature incorporated. Since they did not, we are in perfect agreement that the only source of petrol would be from some form of crack or abrasion in the line from the fuel pump to the carbs.

Few of us take the time to thank the few true professionals who visit this board. Yourself, Paul Hunt, and, sometimes Mark Childers and Bob Thompson. I greatly appreciate your taking the time to post because I learn to much--both what I already know and what I need to study, when you post. Les
Les Bengtson

Hi Les - Thanks for the kind words, I continue to enjoy posting on this board and if I get a little business from it, then that is a bonus!

On the subject of emissions - even the very last cars in the UK had nothing other than the crankcase breather system - NO CATALYTIC CONVERTOR, no air pump (our cylinder heads are numbered differently and never had the drillings for the air injectors - even though our later heads were the same basic casting), no carbon canister, no vapour control. British Leyland were not into using one nut or bolt that they didn't absolutely have to! So US spec cars (esp. California ones) have a lot of extra ironmongery compared with UK ones. We continued to enjoy power outputs of 95 bhp till the end, whereas the power output of the US engines dropped considerably.

In the UK the later cars were (and are) only required to emit less than 4.5% CO and 1200 ppm hydrocarbons (easily achieved on any MGB) - cars first used before August 1975 only need to not emit visible smoke!

And if a car is fitted with a different engine then the rules that apply are the older of the car or engine - so take a brand new car and fit a 1974 engine and you only have to meet the no smoke test!

Chris Betson

Chris,
That's very interesting!

The US, or at least certain parts, take the exact reverse view. If one were to change engines in a car in North Carolina, for example, all of the emissions controls must be fitted, and the emissions standards must be met, for the _newer_ of the two components, chassis or engine...

Just for a comparison as to the emissions standards, for a 1978 Camaro I used to own, the maximum emmissions were 3.5% CO, 350 ppm HC. (That car came from the factory with a 5.0L V8, rated at a staggering 145 horsepower. And just in case all that power made it too quick, it had a slushbox and a 2.41:1 rear end....)

Cheers!
Rob
Rob Edwards

Not me who said UK cars got cats. 4.5% CO together with good running not so easily achieved on my V8 with tubular exhaust and K&Ns even with 'richer' needles, I'm thinking of plumbing in that gizmo that introduces an air-leak at idle and overrun but not when the throttle opens. I have to accept something of a compromise and use the gunsons to weaken it down a bit more before the MOT. Not made any easier by mine being 2% pessimistic compared to the testing station. And my Gunsons Digimeter has packed up which is another bone of contention, seeing as an analogue meter I bought in 1965 still works fine!
Paul Hunt

Paul said,"I'm thinking of plumbing in that gizmo that introduces an air-leak at idle and overrun but not when the throttle opens." What is this gizmo? is it standard on some year models, is it exclusively for V8 cars? Where do we get it? I have to go through British COlumbia Aircare soon, and such a gizmo seems like a breath of fresh air!
Ken R
Ken Rich

Are you referring to the gulp valve?
Rob Edwards

Hi Paul,

You should be able to better 4.5% on the V8.

Mine was way out until I took it for its first rolling road setup - the tuner took quite a lot off the needles - I started out with BAKs in there which was fine at idle but way too weak up the range - he just kept filing flats on the needles till we got 4% at idle and 5% all the way up the range.
Chris Betson

Chris - I got mine with the original BBUs. On the advice of Roger Parker I fitted BAKs which did improve things, making it liveable with the aforementioned fiddling about. I have a graphical needle comparison program and AKN looks a little richer off-idle, BCE a little more so. Any experience with these?

Ken - this is an aftermarket device recently advertised in a number of places including The Sunday Times. There are a couple of web sites describing it and users experiences, which I could post if I could remember the name of the device! It claims improvement in mpg and reduction in emissions, although the users comments I have read claim little of the former but useful amounts of the latter. It is an adjustable spring-loaded valve that opens to the atmosphere when the manifold vacuum exceeds a certain amount, like at idle or on the overrun. It is supposed to be fitted in the brake servo vacuum line but some other way would probably have to be found for factory (at least) V8s as this comes off just one of the carbs and there is no balance pipe other than a very small port in the carb adapter.
Paul Hunt

...or just do what every other beggar in the UK does. Adjust things so that it runs like a pig, but legally, pass the MOT, then retune so it runs right. Sod the Europeans and the horse they rode in on.
Remember, even the boys with the roadside sniffers aren't after you. They're after the 1988 Nissan Sunny pumping out clouds of blue smoke and 24% CO2. That way there's a chance of a conviction rather than a ticking off...
T J C Cuthill

Paul - no experience of AKN or BCE but BAC is probably closer to what I have in my V8 which is a 3.6 on 9.75 CR.
Chris Betson

This thread was discussed between 11/04/2003 and 14/04/2003

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