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MG MGB Technical - Coincidence?

I have had 2 cars in this week with exactly the same symptoms - a misfire under load.

Both owners had assumed it was a breakdown on the ignition side and had replaced parts with no change.

One car had some bits of rubber sitting in the rear carb needle valve seat which reduced the flow into that carb alone - the other had a dirty fuel filter.

Result - at idle and slow speed enough fuel made its way into the carbs and the engine ran normally - under load the carbs ran weak since fuel was not flowing fast enough into the float chambers and the fuel level dropped.

Moral of the story - fit a filter just before the carbs if you have none and change it before it clogs up!
Chris at Octarine Services

Chris-
I agree completely. an in-line fuel filter is the best insurance that you can have in the fueling system. Over here the Purolator fuel filter seems to be the best readily-available choice. What do you recommend for owners on your side of the pond?
Stephen Strange

Most of the usual suppliers sell a clear plastic in line filter with a paper element - cheap and cheerful but does the job.

For the more affluent, K&N do a nice filter or my preference a cleanable filter and pressure regulator as in the pic below

Chris at Octarine Services

Keep a spare filter in the car. Three years ago I broke down, pulled the fuel line off the carb, no delivery. I checked if there was power to the pump, there was, but no clicking. I called the AA out and convinced the mechanic that the solid state pump had given up and to tow me home. He spent about 3/4 hour getting the car up the raised wheel towing system. I spent an hour putting a spare pump on before I checked the filter.
c cummins

"some bits of rubber sitting in the rear carb needle valve seat"

Is this a sign of modern fuel attacking the old fuel lines? Those of us in the UK would do well to consider changing all rubber fuel lines to a modern ethanol resistant type.
Mike Howlett

Rubber does imply hoses breaking down, so that is what should be sorted as Mike says. It is supposed to be 2013 that UK petrol stations can supply up to 10% Ethanol without informing the purchaser of that fact, and 10% is supposed to be harmful to older cars.
Paul Hunt

Ethanol, in the fuel, is the most likely culprit. I've had a lot of breakdowns that can be traced back to ethanol in the fuel where the rubber lines have been degraded. We have a saw mill out back, with a V Twin Honda engine, that refused to start last year. It turned out to be a collapsed fuel line. I had the float fail in the SU HIF 44 carburetor that came with my supercharger system. Ever since replacing the float, I turn off the fuel pump with a cutoff switch under the dash, to run the carburetor out of fuel whenever I park the car for any length of time. RAY
rjm RAY

Ethanol, in the fuel, is the most likely culprit. I've had a lot of breakdowns that can be traced back to ethanol in the fuel where the rubber lines have been degraded. We have a saw mill out back, with a V Twin Honda engine, that refused to start last year. It turned out to be a collapsed fuel line. RAY
rjm RAY

So a fuel filter is not going to help! So which fuel pipes can we use? Are they marked up as ethanol tolerant? Is PTFE stuff ok, although I've always had problems with that stuff getting it to compress and make a good seal.
Allan Reeling

I've used 6mm Goodyear fuel hose instead of 1/4" on my carbs, it fits better and so far hasn't suffered from the malady of rubbish modern rubber of at least the last 7 years
Nigel Atkins

Modern fuel seems to not attack the Smiths hoses or modern fuel hose - I use Codan plain rubber fuel hose.

The hoses most commonly attacked are the stainless braided hoses where there is no cotton reinforcing layer in the rubber. They tend to "crazy pave" with tiny cracks and leak fuel before shedding bits.
Chris at Octarine Services

I have a 67 BGT North American model. I would like to get a filter that will screw in between the fuel pipe and the carburetor lines using the screw fitting. Any recommendations for that?
Bruce Cunha

why not just use the plastic disposable type and renew it each year, just a matter of two clips to replace filter and the filters can be bought for very little price

if you're the cautious type you could even carry a spare
Nigel Atkins

A couple of years ago I suffered a failure of the fuel hose feeding the carburettors. I replaced the original rubber hoses with fuel injection spec SAE J30R9 hose, which I believe is suitable for 10% ethanol fuel.
Brian Shaw

Brian has it right. The important bit of that code is the R9. SAE J30 R6, which is what is mostly sold, is not good enough for ethanol mixes above 5%. It has been quite a problem for rear engined VWs where the engine bay is very hot and there have been vehicles lost to fire due to hoses leaking. See this web page http://www.volksbolts.com/faq/fuelhose.htm
Mike Howlett

I think you're saying that Brian hasn't got it right with the ethanol percentage
Nigel Atkins

No, I think we both are saying the same thing. I'm saying SAE J30 R6 is not suitable for ethanol fuel above 5%, whereas SAE J30 R9 (what Brian says) is fine. Brian says the R9 hose is probably suitable for 10% ethanol, and from things I have read I agree.

I'm trying to make it clear to folks that you need to be careful which fuel hose you buy. The R6 type is extremely commonly sold, but there have been reports of the R6 hose being degraded by E10 fuel. So buy the R9 type which is apparently much more resistant.
Mike Howlett

Codan state that their fuel hose to SAE J30 R6 is suitable for fuels up to 10% bio ethanol.
Chris at Octarine Services

This thread was discussed between 30/08/2013 and 01/09/2013

MG MGB Technical index

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