Morris Minor Owners Club

My 1275cc Morris used to run like a dream on four star, but it hates this Mickey Mouse unleaded fuel that’s been foisted on us. Has anyone else encountered similar problems – and, more importantly, found a solution?

It’s OK on the open road but at low speeds it’s jerky and hesitant, and when creeping through traffic it gets grumpy as the heat rises, the revs fall off and it sometimes cuts out completely (although it will re-start after a lot of cranking). It sometimes runs on when switched off while hot. Yet it used to idle contentedly for hours, sipping four star, when stuck in traffic on the Chelsea Cruise in the old days.

I think the cutting out may be down to fuel evaporation (although the petrol pump doesn’t tick any faster than usual), but I’m also wondering whether an ignition fault would produce similar symptoms? Either way, I’m at a loss to know how to cure it.

The engine is ex-Marina and runs an unleaded head, 1.75-inch HIF 44 carb with a K&N filter, a Mini water-heated manifold, Janspeed headers and a very mild road cam.

I’ve fitted an extended heat shield under the carb and lagged the fuel pipe with asbestos cloth.

I changed the carb needle from a BAZ to a BDL, which I thought gave a slight improvement but now I’m not so sure!

The dizzy has no vacuum advance as standard, the timing is set at 8 degrees BTDC, and the points, condenser, rotor arm, cap and leads are relatively new.

The plugs are dark grey with areas of light brown deposits towards the electrode.

I read than Rob Thomasson was going to try lagging the exhaust manifold on his kit car but I don’t know if it’s cured the fuel evaporation. Has anyone else tried this?

I heard of someone curing fuel evaporation on a motorbike by fitting extra spacers between the carb and inlet manifold to keep the carb cooler. Is this realistic?

What about additives? I noticed a posting on the MMOC site about Tetraboost, which claims to replace the lead content and effectively turn unleaded into higher octane four star. In theory, that would improve combustion but would it prevent fuel evaporation? Does tetra ethyl lead make petrol more stable? Has anybody tried it?

And is this problem peculiar to cars running HIF carbs or do standard cars suffer similarly? Could it be that the greater volume of petrol in the deeper float chamber of the old SU is less likely to heat up? Or perhaps the HIF’s shallower chamber means fuel passes through more quickly so has less chance to heat up?

I posted a similar question a couple of years back and have been experimenting with various settings and suggestions made by members ever since, but without success!

I have no trouble with my 1275 on unleaded. The later side valve engines have a heat proof spacer between the carb and manifold which helps prevent fuel vapourisation.
I would suggest a tune up of the carb

go for the higher octane unleaded ,i run mine on tescos super unleaded its 99 octaine.also have you retarded your timing to cope with the unleaded fuel,it burns a bit hotter.i had problems with it running on when you turned off the ignition.it was set at 8btdc it now set on 3dbtdc.i have electronic ignition fitted and the car has not missed a beat .

Everyone would have this problem if the fuel was at fault, you've got some adjustment issues.

"The dizzy has no vacuum advance as standard"
Cooper S ? Vizard has something to say about these, along the lines of "just because they were fitted to the Cooper Mini doesn't make them a bolt on tuning aid"

I'd suggest fitting a standard dizzy as it likely to be much better in normal driving conditions.

Yes - as I have just posted on another thread - you want a dizzy WITH vacuum advance. This will solve the problem i'm sure.

Thanks guys

I did have the engine Crypton tuned and the ignition retarded from 12 degrees to 8 degrees when unleaded came in.

However, your suggestion to change to a dizzy with a vacuum advance is very interesting. (The dizzy is the original - now rebuilt - unit that came with the engine, which is dates from 1971.

I would assume the Marina dizzy is not interchangeable with a 1098 Minor one?

Does anyone know the model/part number for a vacuum advance dizzy to fit a 1275 ex-Marina engine?

And is there anything about the way electronic ignition works that makes it better at coping with unleaded?

In the meantime, I'll try retarding the ignition a little further.

OK, now I'm stumped!

Just checked the manual for dynamic timing on the 1275 engine, which states that the timing has to be checked while idling at 650rpm.

Trouble is, the old girl won't idle at anything less than 1,000rpm on unleaded!

Suggestions, anyone?!

There were 2 types of dizzy fitted to the Marina. Early ones had a 23D4, like on the Minor ( I'd hazzard a guess that the advance curve is different though), later ones had the 45D4. Neither came with vacuum advance, but the low compression van engine did have vacuum advance.
Not sure about the MG Midget, if they had a vac advance then they might be suitable, as the advance curve should be about right. Might also be worth checking out the Metro 1.3 as well.
On a differnt note, it might be worth trying the engine without the water-heating connected on the inlet manifold (just disconnect the hoses and join them with a bit of copper pipe).
Perhaps the warming of the mixture is compounding the problem?

I changed to an Aldon Dizzy with vacuum advance on my fast road 1275. Expensive,I know,but well worth it. Since the upgrade (together with the "dreaded"electronic ign.) have had no problems whatsoever although the advance curve is steep and timing really needs setting up on a rolling road together with the carb..(HIF44 in my case).There are many cheaper Dizzy's that will do a similar job and I'm sure that other members will advise.Unleaded fuel is definitely not your problem.

Just fit a new 45D dizzy WITH vacuum advance from Simonbbc or Accu-spark -personally I wouldn't bother with the electronic version - but that's up to you. The advance curve may not be perfect - but it will be better suited to modern fuel - and you can adjust it later. Don't worry about 'timing' it - get it running - advance until it 'pinks' - then retard it slightly. Simples! Something sadly wrong if it won't idle slowly - is there an air leak ?

Thanks guys

After reading everyone's comments, I decided to check the fuel and ignition settings but found the engine wouldn't start. Yet it fired up quite happily after I'd fitted a new condenser.

This is the second new condenser in recent weeks. Could this be the source of the engine cutting out when hot? Can condensers get 'cooked' by heat - or the failure of something else in the ignition system? I thought they died instantly, but perhaps they break down gradually?

(I replaced the points and condenser before a long run in Sept but it developed a misfire a couple of miles from home and refused to start the next morning, so the old condenser was refitted. This was OK until I got stuck in traffic last week when things got hot and the engine cut out a couple of times and was difficult to restart. The car ran OK the next day - until the latest non-starting incident today. Coincidence or a pattern?)

Anyway, once the old girl was running I checked the combustion with a Colortune (perfect blue flame), and then adjusted the timing by ear. On the basis of some suggestions, I was expecting to have to retard it still further, but found it ran much more smoothly with more advance. The engine now feels much 'freer', pulls more cleanly from lower revs and ticks over more evenly.

Interestingly, it also restarted instantly when hot - several times.

I've heard that over-retarded ignition can make an engine run hotter, so perhaps this was exacerbating things?

I've yet to experience the heat build-up of dense traffic again but will have to see what happens.

In the meantime, I'll investigate fitting a 45D distributor (do they have the little knurled advance-retard knob like the 1098 dizzies?).

So, thanks everyone - but please let me have your thoughts on the above!

No - no knurled knob - one less thing to worry about! And yes - condensers do fail when hot.

Basically never fill up with Morrissons or Tesco Fuel. Sainsburys use BP fuel, Texaco, Shell, Esso etc are the ones to use. Around here they are the same price as Tesco and mine runs beautifully with it.

very interesting post indeed.

It has made me think further about my own pinking problems since the demise of lrp.

When I set the timing up using static bulb, the timing seems a mile out (over run and pinking under load - made worse on hills). I read recently on practical classics, that many markers for tdc can often be 5plus degrees out due to movement and misfitting - is this relevant to moggies?

Also, when I use super unleaded, I do find the engine runs smoother with less pinking. However I am slightly fearful of retarding the ignition to far for due to overheating. I set up to 3 degrees tdc, then currently end up retading the micro adjuster about 12 clicks. Still pinks a bit mind. any thoughts fromthe experts?

Forget all about 'setting up the timing' with lights/strobes etc - the only way to do it is to set it so it's 'not quite' pinking. You MUST NOT let it pink! However - your problem sounds exactly as if the vacuum advance has failed on the dizzy - have you tested it ?

I tested the vacuum some time ago, but may be worth trying again.
Its quite annoying in all honesty. The engine has the power and decent fuel consumption (41-43mpg), but continues to pink on hills especially - it never use to. I did buy a new dizzy from simonbbc some time ago, however did not put it on as the vacuum was working effectively (12months ago). Maybe time to use it - I have noticed a bit of play in the spindle (excuse the term if incorrect) on the dizzy to.

Fit the new dizzy!

i have noticed when warm my engine runs on a tiny bit. a second after i turn off the key.

also, on fourth gear under load, i hear a resonance that feels like it's coming from the speedo, is that pinking?

otherwise, it seems to pull well on all four gears. not too rich, choke out a little bit sometimes more than halfway and around a mile or less it can go back in again.

If the "resonance" decreases, then stops, as you lift off the accelerator, that's pinking.