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MG Midget and Sprite Technical - HIF 6 gasket - one step forward /back !

Following on from my previous disastrous attempt at fitting a fuel pump following the previous one failing to pump, I finally removed it and on testing it was not pumping (new old stock electronic SU) so I opened the pump and reset the electronic trigger thing and alls well. Refitted and pumped well.

Petrol now flowing out of HIF6!
Removed and checked needle valve - seemed ok and did inverted blow test - all ok - refitted and fuel still pouring out.

On further checking it appears that the rubber sealing ring around the base of the float chamber has turned to a concrete like material ! And fuel was passing through the cover/ carb base joint.

So now need to source new seal rubber - is this the petrol again ?

Also the fuel pipe to the carb which was sold as ethanol resistant is now very stiff as are the braided hoses to the pump !

I’m getting to old for this hassle !

R.
richard b

Richard, you must have missed my post in Les' thread, "Poor idling with 276 cam".


I had the same problem. In the years in storage, the o'ring fuel bowl lid seal, gave up being a seal. My HIF44 carb was never exposed to ethanol, so I think it's just the age of the o'ring rubber.



anamnesis

Guess I did miss the post but I rebuilt this one prior to fitting and replaced all the rubber so its not the original one.

The hoses are now stiff as well so will replace the longer one to the carb when I refit the HIF.

At least its not on my back under the car !

R.
richard b

Ah well that might be bad news for me too then, as I used a new old stock spare I already had, which predates the introduction of e5, so probably isn't e resistant. I'll have to watch for it, but I'm currently using esso 99, so as long as that remains e-free, I'll be ok.


anamnesis

Richard, you'll need to check the cover plate on the bottom of the float chamber. Mine became distorted and the rubber seal would not work. I have tried lapping it on the surface plate, which has improved it quite a lot, but it still leaks a bit. A new cover plate is outrageously expensive at £50 and has been out of stock at Burlen for months.
Les Rose

Thanks Les,
Checked mine and there is a few thou gap at the centre points.
Mine has a lug that stops me trying a plate surfacing - can do edges a bit.
I tried an old ‘O’ ring and by hand pressure the bolt positions on the cover were separated from the carb body by a few thou so hopefully a new ring will be bigger.
I’m not sure the covers were ever machined ?

It looks like the covers are available again and from most of the usual suspects but at a huge cost as you noted.

Will report further when the parts arrive.

R.
richard b

Richard, the lugs are only there to ensure correct orientation. In fact it will only go on one way because of the fuel pickup. I broke the lugs off mine so I could flat the whole thing. Burlen told me that they were doing another production run in July, so I will break the piggy bank and pop over and get one.
Les Rose

Same with mine. If I leave it without fuel in for a few months (engine rebuild etc) then that seal usually leaks. Left with fuel (even e5) in and it seems ok for years. Also have had the distorted base, fortunately I have a spare carb (from when they were £5 a pop only 15 years ago!) so used the one off that.
Great carbs though.
John Payne

Gaskets arrived this morning and fitted.
Fired up and no leaks (touch wood).

While it was warming up a couple of times it cut right out (tach dropped to zero) seems ok know it’s really hot- maybe drying out as it hasn’t been out or run for ages.
Next nice day I’ll give it an outing but intend to run it up a few more times first and wiggle all the connectors/ wipe out the dizzy cap etc.
Any other suggestions?

R.
richard b

Check your breakdown cover?
James Paul

I know Nigel would not agree but I now carry a spare dizzy and leads for a rapid change over !!

Will find my breakdown numbers ! Thanks James !

R.
richard b

Ran it up again today and still had the cutting out suddenly- tach dropping straight down to zero - car immediately restarted each time ?

Tried further wire wiggling etc.

Opened dizzy all looked ok but in a rather vain attempt at trying something I changed out the rotor arm (it was a replacement from Aldon when I had a rotor failure before on a new yellow top dizzy)and again then the engine cut numerous times but did not restart so easily as I recall.
Fitted a new spare Bosch one and it fired up and so far not cut again - I rather think it sounds better but that maybe wishful thinking !
When the weather improves I’ll give it a run and see - it desperately needs a run but not really been able due to circumstances.

I’ve always thought of the tachometer dropping (Guys wise words) as an LT fault, does it still apply with HT I guess it does ?

R.
richard b

Could be ht if the coil to dis' cap ht lead is failing, or the rotor, which you already swapped.

But, -- the rev counter depends on lt current, so ht is not the culpret if the tach stops immediately, and drops to zero. Ht is the output (secondary), lt is the input(primary), and the tach sits in the input circuit.

As you have a complete spare distributor ready to go, I'd swap that in, and see if the fault continues. If it does, then replace the coil. All assuming you don't have an intermittent break between the ignition switch live, and the coil live, or the coil to distributor lead.

Take a new lead directly from the battery live, put a switch in line, and run that direct to the coil. Replace the coil to distributor lt lead too; again an assumption by me that you have points ignition.

As it happens, I'm trialling an aldon electronic in my distributor. AND, as a sensible precaution, I have a complete points distributor in the boot, ready to go if the aldon fails.









anamnesis

Thanks Adam,
Yes that is my understanding of how it works, just trying to work out what would happen if the say rotor shorted.

I’m running a Aldon yellow top dizzy D45 type with an Ignitor module- the original rotor went down and Aldon tested and replaced it with a black one that I’ve now swapped out for a Bosch one.

The leads are visually good being an uprated silicon set fitted by Aldon when they fitted the dizzy some years ago but only a few miles since.

I’ll try again tomorrow and see if it reoccurs.

R.
richard b

Tried again and still cutting out so not the rotor this time !

Swapped out the dizzy for a D25, again with an Ignitor and it seems to have sorted it - been running on the drive for about an hour including various revs etc.

Need to speak to Aldon again on Monday.

Bit late for the sunshine today but should be good to go when there is another nice day - haven’t bothered getting the timing spot on yet but it’s not far off.

Nice when you finally nail an intermittent fault - well mustn’t speak to soon !

R.
richard b

Good luck when you manage to get out for a run Richard. Intermittent faults are so annoying.
Bill Bretherton

Left the car for a few days and the fuel pump failed to proceed again !
Single tick only.
Tried an external feed to pump but no life.

Have now installed a Hardi pump and it’s running again. (Nigel will be pleased!).
The SU on the bench spluttered into life eventually and ran ok - maybe it’s struggling with pumping at start - thinking a stiff hardened diaphragm ? but have not stripped it as yet.

Aldon did a long test on the dizzy and found an intermittent fault and then it failed so now have a new Ignitor fitted. Will refit it tomorrow if weather OK.

Now need some good weather to give it a good run.

R.
richard b

Despite the very over the top prices for SU brand labels they at one time at least had problems with their electronic conversion kits whether this spilled over to their electronic pumps I don't know.
Nigel Atkins

Having checked replacement diaphragm prices as around £38 I think it’s rather a no no !
Rather over the top for a bit of rubber and a rod !

Does Epdm resist ethanol ? - need to check as I have a small stock of sheet.

R.
richard b

Seems great for ethanol but not petrol !
Back to the drawing board.
richard b

Have a look at nitrile rubber. It's available in sheet form and I've bought it off ebay for its oil resistance and apparently good for petrol.
David Billington

Your dead rotor button was probably the initial cause of the ignition module saying enough- Just out of interest, the silicon leads that Aldon supplied are they resistor leads or wire cored---

willy
William Revit

The dead rotor was some years ago and the module ran ok since but finally failed earlier this month.

Out of interest why did you reckon the rotor failure would kill the module ?

The leads fitted were :-
magnecor Electrosports 80 metallic inductance EMI suppressed conductor. All silicon construction SS25 200T !
richard b

Stripped one of the pumps and the diaphragm was hard and stiff as expected so probably the issue.

It seems the diaphragm replacement is not as easy as I had hoped- there is also a large steel ‘keeper/ jumper’ for the magnet to work as part of the diaphragm assembly and it took a lot of careful drilling out to get in bits. Have to have a good think of how best to make replacement parts.

R.
richard b

Richard,

As Willy hasn't responded I'll chip in, my understanding of the issue is that if the HT side can't fire and release the energy then a potentially damaging voltage level can build up in the primary coil which can damage or destroy the switching device by exceeding its voltage rating. It's a reason you should never pull plug caps when an electronic ignition is installed. Similarly taking static handling precautions is good practice when handling modern static sensitive electronic components as they will often not fail immediately but be degraded and fail some time down the line.
David Billington

This thread was discussed between 26/10/2022 and 27/11/2022

MG Midget and Sprite Technical index

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