Morris Minor Owners Club

Looking for a little advice, from the more technically aware...

I have a 1275 'Cooper S'-ish engine in my converted Minor. It's been off the road for over 6 years, then down to Charles Ware's for a floor.

Driving back from Bristol to the Midlands, it was pinking furiously. I have continually retarded the ignition, to the point where it no longer pinks at any speed or under any amount of load.

It feels a little TOO far retarded, if anything, as it's a little sluggish until the revs build.
However...

After a couple of quick back-road trips last week, the car started running-on when turned off. Now it'll do it, within a minute of being started, so engine temperature doesn't seem to be relevant.

There's water in the rad, oil in the engine, far less mayonnaise in the rocker cover than there was, after 6 years off the road - it's had new oil.

Rough spec is: 12G295 head, big valves, fast road cam, single 1 3/4" SU, 1 3/4" LCB - properly built by professionals...

What's going on?

Clues, anyone?

Possibly running super lean, check for any air leaks on the inlet manifold and vac advance on the carb. Has anything been done to the engine since the lay-up, besides the servicing?

Oooooh, I wonder...

I had just noticed that my K&N filter has lost a restraining bolt and there is a LOT of airflow around the loose inner edge.

Mind you, the K&N shouldn't exactly restrict airflow - or so they claim...

I need to order another one anyway, so may have to try taping it together for the moment and see whether that makes a difference...

Since being disinterred, it's had oil and a filter, plus one plug, which died in Bristol.

Probably needs leads, plugs etc as well...

And really, REALLY needs a rolling road tune...

Surely that head is not for a 1275! The largest unit it was fitted to was 1100

The leak would have to be on the manifold side of the carb to cause a problem. Start the engine and feel around the joints to see if there's any sucking air in and make sure the little vac line is attached at both ends. Another way to find air leaks it to squirt WD40 around the joints, if it gets sucked in you will hear a difference in the engine note - and possibly a slurping sound

les wrote:Surely that head is not for a 1275! The largest unit it was fitted to was 1100

I may well be completely wrong... 12G940?

The engine builders were extremely well respected Mini racing guys - the chap who built this engine was a Miglia champion - so whichever head it is, it is a pukka job... not some bitza hacked together by myself!

My memory is about as lacking as my current Minor-ing skills...

It's been rather a long time since the Pram has been used regularly and I'm a lot rustier than the car is now!

panky wrote:The leak would have to be on the manifold side of the carb to cause a problem. Start the engine and feel around the joints to see if there's any sucking air in and make sure the little vac line is attached at both ends. Another way to find air leaks it to squirt WD40 around the joints, if it gets sucked in you will hear a difference in the engine note - and possibly a slurping sound

Hmmmmm...

Will give that a try...

les wrote:Surely that head is not for a 1275! The largest unit it was fitted to was 1100

The engine they built for my racing Mini Se7en revved to 8000 and always came back for more... The Minor engine is conservatively redlined at 6000, for road use... it gave 95bhp at the wheels on Peter Baldwin's rolling road when newly-fitted and not run in.

940 is more like it, yes. The latest cooper s was fitted with a version of that, the original heads although better flowing, were prone to cracking.

You will need to use top grade petrol - perhaps the fuel in the tank has deteriorated? And check the vacuum advance is working.

bmcecosse wrote:You will need to use top grade petrol - perhaps the fuel in the tank has deteriorated? And check the vacuum advance is working.

It actually started on old petrol a few months ago, to drive onto the trailer for moving to CWMM...

However, it has gone through several tanks of fresh fuel since re-emerging with an MOT...

I shall try to make sure I only use Shell Advance or similar... I wonder if a good shot of octane booster would make a difference? Might have to try that...

Electronic ignition and water-heated manifold - not sure if there is still a vacuum tube... will have to go and poke my head back under the bonnet tomorrow...

Although, as it's not hissing down with rain, am I legally allowed to try fixing an old car???

You'll get nicked my son

The inlet manifold should NOT be water heated. You want the ingoing gases to be as cold as possible. Vacuum advance is essential - it was muddled thinking that eliminated it in the S engine. To 'run on' there must be something glowing red hot in the combustion chamber - perhaps wrong grade of spark plugs? With the spec you give, I suggest Champion N6Y will be appropriate.

bmcecosse wrote:The inlet manifold should NOT be water heated. You want the ingoing gases to be as cold as possible. Vacuum advance is essential - it was muddled thinking that eliminated it in the S engine. To 'run on' there must be something glowing red hot in the combustion chamber - perhaps wrong grade of spark plugs? With the spec you give, I suggest Champion N6Y will be appropriate.

I was assuming something would be way too hot... I suspect the replacement plug may be the problem... but like everything else on the car, those definitely need changing...

There are different views about water heating the inlet manifold - for maximum power, the consensus is that it should not be heated, but for general ease of running, especially in the first 5/10 minutes from cold, a water-heated manifold will ensure that the atomisation of the fuel is more even, with minimal condensing of the fuel on to the cold manifold surface. This is one of the causes of hesitancy whilst warming up.

The atomisation process itself produces a cooling effect within the inlet manifold, and without heating it can, in cold conditions, lead to icing up of the manifold, even in the UK.

The next time I have a rolling road session, I will try to do a back-to-back power comparison between a heated and non-heated inlet manifold. The water system on our 1380 engine has the heater in circuit permanently, fed from the back of the head, then down through the MG Metro water-cooled oil cooler, before returning to the bottom of the radiator, à la standard 948 heater hose layout. The water tap only controls the heated manifold, which normally is 'on'.

What plugs are fitted? A standard Minor uses Champion N9Y / NGK BP6ES; the next grade up (cooler/harder) is N7Y/BP7ES and then N6Y/BP8ES, but I would think that the N7Y/BP7ES should be right for your engine. I use BP7ES and apart from a long ago saga with local overheating caused by no by-pass hose, they have been excellent. I do have an anti-diesel valve from an MG Metro fitted, but there is no run-on, so I'm not sure whether it ever needs to do anything.

During the first 5 to 10 minutes of running - the water is cold - so it has no hope of heating the inlet manifold..... None of the twin carb inlets have water heating, and they seem to manage ok...... Indeed - in the case of the 'tiny twin' 1.25 " SUs -it's pretty much the ONLY advantage over the single carb - the elimination of any heating of the ingoing mixture.

As I said - different views!

The manifold does not need to hot, just not cold, and the temperature gauge on ours is on the move after a minute or 2 - it is in the standard position on the side of the head, so sees the quick build-up of water temperature with the thermostat fully shut. The inlet manifold is also fed permanently, thermostat shut or open, so sees a warming effect very quickly.

Yes, Richard, the anti-icing requirement for some engine/carb/manifold set ups.

I recall a work colleague fitting a minnow fish carburettor to, I think, a Cortina for extra power, in the late 60s. It actually needed a heating grill in the intake to avoid icing at start up. Many cars either took air from around the exhaust manifold to aid winter running - intake had a second position for summer running. IIRC, the MKIV Cortina had a thermostatic change over or something? I know mine iced very badly back one winter morning in the early 80s. The venturi was almost closed with ice! The temps dropped to around -20C that morning.

Some zenith replacement carbs ice up easily on some versions of tractor I have, even in warm weather.. Never a problem with the original Marvel Sheblers.

Mk 1 cortina GT engines always had a water heated manifold (with the Weber DCD 28/36). They did not have that arrangement for no good reason! A cooler, more dense, air charge is better, but no good if it ices, or even condenses the fuel on the manifold surfaces.

One has to remember that it requiress 80 times the heat removal to freeze water than reduce liquid water (or vapour) by 1 degree Celsius. Overlooked by design engineers at their peril!

RAB

Amazing how the twin carbs manage at all.....