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MG MGB Technical - Fuel filter to carb connection

Hi Guys,

I have mgb roadster 1980. Some years ago i changed all the fuel lines to copper (which is 5/16 or mm equiv) up to the fuel filter having previously got through two sets of steel having had the car from new. I have recurrent problems of a fuel leak on the exit side of the fuel filter which is 5/16 and the connection (via a short piece of rubber hose ) to the copper pipe that is attached to the inside wing (which is 1/4 as replaced at another time - supposedly being a direct replacement in terms of size for the original mild steel one) before a final rubber hose section that connects it to the front carb.Despite using the smallest clips possible to prevent distortion these leaks keep occurring. A simple solution would be to dispense with this 1/4 copper pipe and use 8mm (5/16) petrol hose from the exit side of the fuel filter to the front carb. (In the original spec i think the whole system might have been 1/4 including the fuel filter ends which simply needed the factory fitted clips to be squeezed with a pair of pliers to enable the rubber hoses to be pushed on / pulled off).

Is it essential that i keep this final section of copper fuel line ? (The original plastic cup clip is clearly designed for a 1/4 pipe to attach it to the inside wing).

An alternative would be to some 5/16 copper pipe or use a step - down union from between the fuel filter and the 1/4 copper pipe - i was trying to avoid having yet a further set of connections / small pieces of rubber etc!
CMD FARRAN

I'm surprised you have had to replace steel lines twice, as far as I know both 73 and 75 are still original.

I believe it is a different size one side of the filter to the other, on the V8 I remember filter having two different diameters at each end, and using the lager inner one to get to the main pipe and the outer narrower one to get to the carbs. I've also seen a 5/16" to 1/4" reducer used in various places.

There must a defect in one half of the leaky joint or the other, a hose clip doesn't have to clamp with exactly equal pressure all the way round the hose, the rubber in the hose itself will take up a certain amount of unequal pressure.

I'm assuming the leak is from where the filter hose joins the pipe that leads to the front carb. A hose from the filter all the way to the front carb would be no help. Where did the pipe come from, was it cut off a roll?

Then again, I'd expect a defect in either hose or pipe to leak immediately. Usually once tightened and not leaking, it will continue not to leak until the hose rots or something else breaks down.

I see no reason why you couldn't use hose all the way from the filter to the front carb - if the leak is between hose and pipe. The V8 is like that, but then again it is a shorter run as the carbs are at the rear of the engine compartment.
Paul Hunt

Hi Paul,

Sorry i meant the brake lines!

The first set of steel lines were replaced as i was advised that it would give rise to a possible MOT failure the next time one was due. I decided the next time i saw evidence of rusting that i would replace them once and for all with copper - not essential at that time but i thought expedient - i don't regret it and shortly afterwards changed the fuel line for copper as well.

Back to the problem:-

The filter has the same size diameter at each end which is 5/16 - hence no problem at all on the supply side as it connects to the line running from the fuel tank. My reasoning for dispensing with the final section of smaller copper piping is that the leak comes from the "copper pipe end" of the rubber hose that connects it to the exit side of the fuel filter. (I proved this as my son turned on the ignition to start the pump whilst i had my head under the bonnet)!

The 8mm (5/16) rubber fuel pipe was purchased off the roll (i saw the parts bloke cut it off) new last week from Sureparts in Redditch.

The leak came from exactly the same place as before i replaced anything. (I replaced the small section of hose each side of the fuel filter as well as the fuel filter itself).

CMD FARRAN

What hose clips are you using? If it's those spring types, that you squeeze to get on / off, then they will leak. Use the worm drive type and you can tighten them up as much as you like.

Herb


Herb Adler

Herb,

Thanks for your comment - I'm using clips with a bolt & nut that i can tighten down with a small socket, but still get a problem. (The spring type are not strong enough to pinch down the rubber hose - these modern petrol hoses all seem to have additional inner strengthening (& therefore hard to compress) - i guess for high pressure situations which i don't think is needed where carbs are concerned).
I seem to recall the OEM rubber petrol hose from the fuel filter to the 1/4 copper tube on the inside wing was the same as the rubber hose that links the two carbs together (which is held easily by two spring clips that i used again quite successfully when that hose split for the first time about 3 years ago, having had the car from new since 1980. That hose seems to be the same as on my atco lawnmower)!

Charles
CMD FARRAN

Try locating a fuel filter that has 5/16" on the inlet side and 1/4" on the outlet side. My Moss supercharger system came with one. I still have the original metal fuel line, running from the fuel pump to the filter, in my '67 B. The only reason that I replaced my original brake lines was due to their being almost a half century old. I used the Cuprinol lines that are 80% copper and 20% nickel. RAY
rjm RAY

IIRC the original peice of inner wing pipe had an enlarged end that was 5/16 leading to an 1/4 pipe so that there were no issues with the filter.

That being said, you can dispense with the pipe and just run a 1/4 bore rubber from the front carb onto a suitable filter. A lot of the cheap plastic ones I see have a double barb where you simply push a 5/16 on further and the first step is for 1/4 bore. Actually it's 6mm and 8mm, but that'll do.

http://www.ebay.co.uk/itm/2x-Line-filter-fuel-filter-universal-6-8-mm-pipe-fitting-/251844596887?pt=LH_DefaultDomain_3&hash=item3aa31b9497

That's the type of thing you're after. Hope this helps.
Roadwarrior

Many thanks to all! - the solution was really staring me in the face - highlighted by Paul's comment that he remembered the filter "having two different diameters at each end" which Roadwarrior had also seen. The one Roadwarrior gave me a link to is in fact the type i am using.
As my replacement copper tube on the inside wing is 1/4 with no enlarging at the end (which i would like to keep in place) i intend to purchase some 6mm rubber fuel hose to connect it to the smaller diameter section of the exit side of the fuel filter.
Need to get it done this week as my "3 yearly valuation for insurance" is due in the first week of March and as my drive slopes up to the garage , i can't just push the car out for photos & then push it back in again!
CMD FARRAN

I've previously had a lot of trouble with 1/4" fuel hose, being one of the p*ss-poorly made rubber parts so I bought modern 6mm

I can recommend G4509 Goodyear Fuel/Emission - DIN 73379-1 - 6.0 mm X 3 mm - 2B >NBR/PET/CSM< - and it was a better fit to the carbs than the 1/4"

I've used the plastic disposable fuel filters for many years, changing at annual service, the ones with both sizes at each end
Nigel Atkins

Thanks for your recommendation Nigel!
CMD FARRAN

no problem, I got mine off-the-reel a couple of years back from Halfords, I'm not sure if they'd have it now but many good motor factors might, another good quality brand modern 6mm would probably be just as good
Nigel Atkins

I hear that all fuel components’ have to be ethanol compliant now.
J Hughes

All fuel components SHOULD be ethanol resistant but clearly are not. Huge amount of misinformation out there, tho it has to be said there is almost no evidence (that I can find) that proves conclusively that ethanol has actually been identified as the cause of a problem.

FWIW SAE J30 R9 should be ethanol resistant to 15%

More here http://www.mgb-stuff.org.uk/fueltext.htm#refurb
Michael Beswick

But they aren't all ethanol fuel compliant. Fans of the VW beetle and bus have been struggling with fuel hose for some time. A number of these air-cooled wonders have been destroyed due to failure of rubber hoses in the extremely hot engine bay.

The common hose offered was marked R6 and you can still buy it now, but it is not totally proof against ethanol. Better is the hose that is marked R9, but there have been some reports of softening with that where fuel is E10 or above. See a table describing the hose types here http://www.volksbolts.com/faq/fuelhose.htm

I ended up using R9 on my MGB V8, but on my Lotus Elan I have used this stuff http://www.vwaircooledworks.co.uk/Fuel-Hose-Kit---Full-details.html which is supposedly proof against 100% ethanol. I purchased a single carb kit and had plenty for what I needed.
Mike Howlett

Depending on what you read SAE J30R9 is suitable for E10 or E85 or 100% ethanol or 'not for bio fuel'. This document http://www.volksbolts.com/faq/SAEJ30.pdf talks about R9 having a permeability of 15 grams per meter squared per day with E15 whereas R6 has 600. But then the test with E15 only lasted 70 hours! That doesn't give any indication as to longevity.
Paul Hunt

Guys,

I purchased 6mm hose from Halfords yesterday & fitted in the manner previously discussed and am pleased to report no leaks!!!!!!!! My biggest problem was finding stockists of 11-13mm petrol pipe clips as the ones stocked by Halfords were either just undersized or oversized. I ended up trying at Sureparts in Redditch where all their clips whether it was in packaging 11-13 or 12-14 actually contained 12-14!!! Reddispares had none but a flimsy alternative, Car Spares in Longbridge had something close,but not ideal. I eventually got i pack(containing 2)from europarts in Kings Norton and another pack from europarts in Acocks Green (the only pack they had)!
With the proper clips job done in 15 minutes!!!
I think i should have waited until Stoneleigh this weekend!
Thanks again to all.
CMD FARRAN

Ray, your recent post made me smile when you wrote about "Cuprinol" cupro-nickel tubing. In the UK the trade name for this product is "Cunifer".
Cuprinol is a trade name for a brand of wood preserver.

regards John
john wright

Well, John, I must be using wood preservative for my brake lines! Who knew? Actually, in the States, we also have the same brand wood preservative. Getting back to Ethanol resistant components, I've personally had the float fail in my HIF44 carburetor. It had a hole eaten in the side. I've also encountered quite a few fuel lines that have collapsed internally due to being dissolved by Ethanol. It's a stupid way to make quick money for farmers who would otherwise be planting their fields to grow food to feed the world instead of our cars. It produces less power and more headaches. RAY
rjm RAY

Hello Ray,I have also had ethanol issues, the fuel pipe between the carbs split, I put it down to ethanol, but it may be old age, the car I mean. One day last summer I turn the ignition on and the pump was going mad, so i turned of the ignition and had a look under the bonnet(hood) and there was petrol all all over the exhaust manifold, good job the engine was cold or would have been goodbye MGB and goodbye garage and maybe the barn that the garage is attached to. The fuel pipe had a split about 2" long!!!!

regards John
john wright

This thread was discussed between 21/02/2015 and 26/02/2015

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