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Stromberg 175 CDSEV Diaphragms – How resistant are they to modern fuels containing ethanol?


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The last pair of diapragms I fitted to my California spec car only lasted 2 years before splitting, over which period the car covered less than 10000 miles. It got me wondering about the quality of the rubber and the effect of modern fuels.

The Triumph TR6 Repair Operation Manual (brown book) recommends the Carburettors are overhauled every 24000 miles to keep them in good order. But that advice was published in 1976 long before fuels containing ethanol became common place.

Burlen Carburettors in Salisbury England, supply diaphragms made from Hydrin which is a high quality rubber but as ethanol levels in fuels are rising, how long do Stromberg diaphragms typically last now and so how frequently should they be replaced?

For example, should I be thinking of routinely changing the diaphragms annually/after 5000 miles whichever is the sooner to mitigate the impact of modern fuels?

What are other users experiences? I’m particularly looking to our friends in the USA for comments.

Martin

 

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I rebuilt the twin Stromberg CDSE 150 carbs on my GT6 nearly 20 years and 30k miles ago. Fitted new diaphragms back then, and they have been fine ever since. I wouldn't worry too much about the effect of modern fuel on the rubber of the diaphragms 

Nigel

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Diaphragms are cheap  enough and easy  to swap out to carry a spare if they do split. They are only in contact with air rather than fuel so I don't think they should be effected   much. I have had no issues in the last 3 years running Strombergs on unleaded.

Paul

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Nigel, Paul

Thank you for your encouraging comments.

I didn’t think the fuel came into direct contact with the diaphragms.

However during last year’s hot summer (certainly in the SW UK), the TR6 under bonnet temperatures were often very high, so much so that I experienced vapour lock several times and so wondered about the effect of ethanol fumes rather than liquid fuel.

I now doubt the quality of the two diaphragms I originally fitted. I can’t recall the supplier except to say they weren’t from Burlen, so perhaps the quality wasn’t up to scratch.

BTW the split diaphragms caused a drop of over 15HP at the wheels when the car was tested/tuned on a rolling road this week so I’ll definitely be taking spares to Europe this year.

Martin

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Most of the TR6's here in the US are using E10 fuel and I am not seeing any issues with the Strombergs beyond normal wear. I think at this point all of the rubber in the fuel systems has probably been replaced. Fuel lines, fuel pump, carbs.

Stan

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  • 2 weeks later...

Thanks for your comments Stan. That’s very reassuring.

As well as packing spare diaphragms for our European trip, as an added precaution, I’ve now also fitted a stainless heat shield from Moss to lessen the likelihood of vapour lock reoccuring since UK motoring organisations report “Ethanol's higher volatility can contribute to 'vapour lock' issues in older vehicles when operating temperatures are higher”.

Which they will be in July in Italy no doubt.

Fingers crossed and thanks.

Martin

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I ran my old Stag as daily driver for 8 years until 2014 , it was fed just about all brands of unleaded and the diaphragms of the Stroms never degraded at all in that time.... I dare say they’d been in for a few years before my ownership as well.

....... Andy 

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FYI 

from the Esso website   - https://www.esso.co.uk/fuels-faqs

 

Regarding Ethanol - I tend to use the Esso super unleaded - Sunergy Supreme +-  in all most everything that I own with a engine (including the Suffolk Punch ....) Personally I feel anything that gets laid up (or little use) over winter would benefit from this (I believe the Ethanol element in unleaded is hygroscopic  and therefore absorbs moisture from the air) 

This was after having to rebuild the carbs on my MGA including most of the rubber fuel pipes.

 

"other fuels are available" but I have no idea if they contain Ethanol

 

 

"The majority of unleaded 95 Octane petrol sold in the UK contains up to 5% ethanol as required under the Government’s Renewable Transport Fuels Obligation (RTFO).

There is currently no requirement for renewable fuel (such as ethanol) to be present in super unleaded (97 grade petrol).

Esso super unleaded petrol (Synergy Supreme+ Unleaded 97) is ethanol free (except in Devon, Cornwall, the Teesside area and Scotland). We would therefore advise anyone who has concerns about the presence of ethanol in petrol to use Synergy Supreme+ – providing they do not fill up in Devon or Cornwall, the Teesside area or Scotland.

Our Synergy Fuels:

Diesel

Supreme+ Diesel

Unleaded

Supreme+ Unleaded"

 

Matt 

 

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Matt thanks for that.

If your lawn mower has twin Strombergs, no wonder its called a Suffolk Punch.

Yours must be the fastest lawn mower in Somerset by a country mile. ;)

Martin

 

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