Morris Minor Owners Club

The engine does sound like its hunting at idle, but no matter what adjustment i make on the fuel mixture revs dont come up or the engine idling smooth out.

Sounds like that carb has seen better days!! Swap it and let us know the results. Sounds like the adjuster is knackered. Have you checked the jet by looking at it yet?

The engine idle spped is controlled by a different adjuster from the mixture. You may need to adjust the two together to get a reasonable idle. Apologies (& red face) if you've chacked that..

Colin

Thing is, that we are not after a reasonable idle, there are far more serious problems here!! As you say, if that were the case a simple screw adjustment would cure it.

If the mixture is off then the revs will drop. They rise when the mixture approaches the correct setting, regardless of the idle screw (which just acts as an adjustable end stop on the throttle cam). If you start messing with the idle screw as well, you might end up confusing yourself.

Is the mixture adjusting NUT approx twelve flats down from the
'right up' position? If not then adjust it to that setting. As you weaken
the mixture(less than twelve flats) the tickover speed should increase.
if you enrich the mixture(more than twelve flats down) the tickover
speed should decrease. If you cannot attain this condition then
your needle may be too high or low in the piston. The fact that your
tickover speed increased when you disconnected the vacuum pipe
is correct. You could also have a sticking piston which does not
fall down to hit the bottom as it should do, remove the air filter and
lift the piston with your finger(engine off) the piston should fall with
a soft plop as it hits the bridge. If it doesn't then either the piston
and housing need cleaning(no abrasives) or the needle is binding.

Is the mixture adjusting NUT approx twelve flats down from the
'right up' position? If not then adjust it to that setting. As you weaken
the mixture(less than twelve flats) the tickover speed should increase.
if you enrich the mixture(more than twelve flats down) the tickover
speed should decrease.

Willie, he's using a HIF carb, so there is no adjusting NUT, but an adjusting SCREW.

Hi everyone, hope u had agood weekend. I gone through some more checks on the car. Ive examined the spark plugs more indepthly. It seems that 1 and 2 are white and blistered indicating overheating. Plug 3 which is a slightly older plug as the other broke is brownie/ black incolour and plug 4 is grey to brown in colour. I tried removing the engine breather pipe and there is no difference with my finger over the tapping, but with my finger removed revs decreased by approx 50-100 rpm. Removal of the vacuum vacuum advance still increases the rpm but im wondering that the tapping location above the throttle valve acts as if the throttle is being increased by letting more air in.
Ive regapped and cleaned the plugs which seemed to improve matters somewhat but soon the engine played up.
I have cheched the compression on all cylinders and the compression is fine on all four.
I noticed that the problem is very much temperature related as the problem doesnt occur until engine pressure is down to 40 at idle and the oil is fully warmed up.
My next investigation will be more indepth look into the carb it self, i.e warn dashpot.

Well........... that kind of changes things.
If 1 & 2 are white and 3 & 4 are normal/rich then due to the siamesed nature of the head, you are lean on the front intake port of the head and normal/rich on the rear one. The carb has been eliminated as cylinders 3 & 4 are fine.

It is more than likely an air leak from the inlet manifold to the head on the front intake port. Take the manifold off and look at the gasket. See if it has an even indentation of the inlet manifold in comparrison to the exhaust manifold adjacent to the port in question and also the other inlet/exhaust flanges.

Would be the problem even though it doesnt happen until the engine is fully warmed up. I assume if the plugs were overheating that they would do this quite soon after starting the engine

Well, if all 4 plugs are the same heat specification / make etc, then you are leaning out on the front 2 cylinders. The front 2 cylinders are fed from the front single port and the rear two are fed from the rear single port.

The rear two cylinders are fine (according to your plug colour description) and the front two are running lean (again according to your plug colour description), so the front port is getting a weaker mixture than the rear.

The mixture splits evenly at the carb and 1/2 goes to the front port and 1/2 to the rear (even though the cylinders 'suck' on the carb in sequence). So there is a problem between the carb exit and the inlet port on the head. This is causing the mixture to lean out. The reason for a lean mixture is a lack of fuel compared to the amount of air, this would happen with an air leak, as the suction pressure on the carb would not be as great due to the leak letting in air. So, have you checked the areas that I mentioned above??

Sometimes the flange on an alloy inlet manifold is a different thickness to the flange on the exhaust manifold. If the inlet flange is thinner, then it won't pull up to the head properly and won't seal properly. I would seriously check this out before proceeding.

With regard to heating, maybe when cold it is JUST sealing, then when it gets hot the exhaust manifold expands slightly and loosens the 'grip' on the cooler alloy inlet flange creating the air leak.

If you take the inlet and exhaust manifolds off and look at the gasket you should see the indentations. It might be a good idea to put 2 gaskets back on when you re-assemble it as these will indent more, sealing the gap. BUT examine the flange thickness to see if this is the problem first!

Hey everyone. I took off the manifold at the weekend and examined the flange thickness which seems fairly the same on both inlet and alloy outlet. I tried using two gaskets as cam suggested but this has made no difference. I earlier said that the engine seem to hunt badly once warmed up. This seemed due to a float level too high. This is becoming a real pain. I adjust the mixture to enrich it slightly therefore reducing the pinking but then the engine doesnt idle evenly and vice versa. The carb seems in good nic and had been working perfectly until this situation arose.
Could the problem be due to carbon in the piston chamber. Would this take time to overheat.
Im wondering whether faulty plugs could be the problem and arent dissipating the heat effectively.

Well, the problem is that the front cylinders are getting a different mixture to the rear cylinders.

If it were a carb problem then it should be apparent in all cylinders.

The carbon build-up would aggrivate pinking but would not cause your plugs to run white......

If you still have two rich cylinders and two lean cylinders then there must be a leak somewhere inbetween the carb and the head.

If it were purely a carb issue then all cylinders would be affected. Same as if the plugs were the incorrect grade (assuming they are all the same).

I suppose it IS possible that you have a cracked cylinder head, but probably unlikely. I personally would swap the carb and manifold with another known working set and see if the problem still exists. If it does then you have eliminated the carb and manifold out of the equation.

Hey everyone.Ive had success in getting rid of the pinking problem and the poor performance. I checked everything as suggested but found nothing. I took off the head and it was very very clogged up with carbon. Much of the head and the top of the cylinders were completely fouled. After cleaning this all off everything seems alot better. I did notice that some of the inlet vlave could potentially be slightly pitted and the seats were in need of some work too. Next time i got some time and some money ill reprofile the seats and maybe get new valve.
I spose the reason for it being so bad is that the car had a number of air leak problems a couple of months ago including a hole in the vacuum advance diaphragm.
What is the best way of cleaning carbon out of the engine without taking the head off again. Is there somesort of stuff i can buy or some sort of trick. Ive read on the net that someone suggested strayinging water into the mouth of the carb whilst the engine running to effectively steam clean the combustion chamber. Is this wise??

The only way I know is the hard way, I'm afraid! I've never heard of spraying water into the inlet, and can't imagine it would work, but always happy to be proved wrong.
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What ive read is that you run the engine hot and apply a trickle of water through the carb throat whilst maintaining the revs and the water evaporate in the cylinder on combustion and its suppose to steam clean the inerds!!??

I'm afraid! I've never heard of spraying water into the inlet, and can't imagine it would work,

Neither have I its hard enough to get the carbon of with wire brushes in a drill as it is.

Blimey - as I say, someone may have heard of it/tried it, but instinct would make me reluctant to!
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I'm with Andrew on this one. It just 'feels' like a bad idea.

Holts used to make a product for decarbonising without dismantling. It was in a tube and with the engine hot the stuff was squeezed from the tube into each cylinder through the plug hole. Then left overnight I think. Did use it once years ago and it did seem to have a limited effect. There was some serious black rubbish pouring from the exhaust for a couple of miles anyway.
Never heard of the water thing for dispersing carbon deposits in an engine but the exhaust gas side of medium to large turbochargers are cleaned by water washing though. Has to be done at low revs so as not to damage the turbine blades.