Carb to pump fuel pipe attachment diameters

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nwxh
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Carb to pump fuel pipe attachment diameters

Post by nwxh »

I just tried to attached a new fuel pipe after the previous one came off while driving and showed signs of damage.

I got an official SU ones, hoping it would be the best: https://www.morrisminorspares.com/fuel- ... ps-p830611

However, while the tube attached the carburettor without issues, unfortunately it broke on the SU pump. Essentially the attachment pushed peeled back the rubber on the inside.

I measured both attachment diameters: the one on the carb was 6.49mm, so just above 1/4" but the one on the SU pump was 7.13mm so just over 7mm. Is this a known issue? Is there a way to replace the one on the SU fuel pump with the same 1/4" diameter, or even to switch this for a more secure fitting of some kind.
ManyMinors
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Re: Carb to pump fuel pipe attachment diameters

Post by ManyMinors »

I must admit that there is no way I'd spend £50.00 on an "official SU" fuel hose :o and I just bought a length of proper modern rubber fuel hose from a local motor factor for about a tenth of that :wink:
What a nuisance you've had such trouble.
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geoberni
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Re: Carb to pump fuel pipe attachment diameters

Post by geoberni »

I don't understand how an additional 0.64mm on the diameter would cause such a problem. That's around 10% increase, hardly a lot when dealing with a rubber hose.

Ever curious, as I knew mine had gone on easily enough, I just went out and measured it. I've only got a cheap electronic vernier, but my readings at the pump outlet fitting were:

5.50 mm at the tip,
7.70 mm at the bulge,
7.10 mm at the main part.

So quite similar, but have you got the reduced diameter at the tip?
20220401_152410.jpg
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nwxh
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Re: Carb to pump fuel pipe attachment diameters

Post by nwxh »

Mine does not have a bulge. It also comes directly vertical from the pump while you seem to have some fitting with a barb (so more reliable). Mine looks just like the one on the SU website: http://sucarb.co.uk/su-fuel-pumps-spare ... -9039.html See the upwards pointing brass attachment and not how little taper it has.

I would buy the fitting you have if I could be sure that it would fit into the pump body (have to have same thread on that side or I'd add to the problems). Also, mine had very little taper: I would almost certainly have been fine with yours as the taper is 5.50mm at the narrowest point. It looks like yours is similar (or the same) as the tube I tried.

It's possible that the product, despite being expensive, is not fit for purpose. One problem is that you cannot see the tube you are putting on as it's effectively a long tube with braid around surrounded by a 2cm or so bigger tube which covers the braid, with the long tube being recessed about 1cm. So you are pushing it on blind hoping that the inner tube wraps the attachment. One side fitted in fine but the other got caught, the rubber preferring to peel down rather than expand. Of course if there was more of a taper it would have worked better.
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geoberni
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Re: Carb to pump fuel pipe attachment diameters

Post by geoberni »

I must admit I have no idea as to the provenance of mine, I've had the car 5 years and the pump was in place many years before that.
It's the sort of small detail you don't immediately notice but thinking about it, most cars seem to have a straight fitting on both pump connectors.

Perhaps someone else can help.
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philthehill
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Re: Carb to pump fuel pipe attachment diameters

Post by philthehill »

This is the straight fuel pump outlet connector for the Morris Minor fuel pump.
SU pump connector.JPG
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The O/D of the straight push on fuel pump outlet is 9/32". Therefore a 1/4" I.D pipe will and should fit without any difficulty.
It is best to undo and slide the clip off the rubber end sleeve towards the middle of the pipe and re-fit the clip after the pipe has been fitted to the straight fuel pump outlet. If you do not move the clip off the rubber end sleeve the possibility of the inside of the flexible pipe being rolled back is greatly increased as has been found.
Giving the fuel pipe a good wiggle when fitting will assist the pipe to feed over the outlet pipe.

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Re: Carb to pump fuel pipe attachment diameters

Post by ManyMinors »

Bernie's car is a Series11, which originally would have had different fuel hose attachments to a Minor 1000 type which is what Phil's picture shows.
That explains the difference.
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geoberni
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Re: Carb to pump fuel pipe attachment diameters

Post by geoberni »

Yes, as my only experience of Minor Ownership is my SII, sometimes the differences with latter cars are totally foreign territory to me.
The Workshop Manual for example, has Section B for MM Fuel system, BB for SII and BBB for 1000.
They obviously didn't feel that it was worth a mention in the manual that the union had been changed.
So Section B illustrated the Pump for the MM, with reference to cleaning the points and coincidentally shows the union, but that's all.
Pump.JPG
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But AKD3541, Service parts List for the 1000, shows the straight coupling.
Seems a bit of a retrograde step, it perhaps was a cost cutting measure.
.
Pump 1.JPG
Pump 1.JPG (69.66 KiB) Viewed 1080 times
.
Holden offer Elbow Unions, I'm sure other providers must do too.
https://www.holden.co.uk/p/elbow_kit_for_lp_fuel_pumps
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nwxh
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Re: Carb to pump fuel pipe attachment diameters

Post by nwxh »

Looks like all the push on fittings offered by Holden have one or more barbs, except those for SU pumps. :(
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Re: Carb to pump fuel pipe attachment diameters

Post by philthehill »

For the Minor which has a low pressure S.U. fuel pump - barbs are not required.
There is enough grip provided by the tube itself and the securing clip.

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Re: Carb to pump fuel pipe attachment diameters

Post by nwxh »

With the new pipe, it holds even without clips. I made sure to only do the clips up until they wouldn't turn around on the hose so hope it's tight enough without being too tight.

Although it has been working fine, I did a motorway test and it seemed to misfire now and then at 70 MPH but was fine at 60 MPH. Could it be fuel starvation at that speed or an unrelated igniton issue. The car did vibrate a bit more than in the past (balanced prop shaft or new diff needed?) so that could be an issue.
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Re: Carb to pump fuel pipe attachment diameters

Post by oliver90owner »

nwxh wrote: Thu Apr 07, 2022 10:29 pm With the new pipe, it holds even without clips. I made sure to only do the clips up until they wouldn't turn around on the hose so hope it's tight enough without being too tight.

Although it has been working fine, I did a motorway test and it seemed to misfire now and then at 70 MPH but was fine at 60 MPH. Could it be fuel starvation at that speed or an unrelated igniton issue. The car did vibrate a bit more than in the past (balanced prop shaft or new diff needed?) so that could be an issue.
A possibility of a dying U/J? Wheel balancing? Tyre construction? More likely issues, in my book.
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Re: Carb to pump fuel pipe attachment diameters

Post by nwxh »

U/J is a possibility. Wheels should have been balanced just over a year ago: at least one has visible weights.
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