Temperature: Above Normal or Just Average?

OK thanks for the photo, good to rule this out. As a matter of interest do you know how old the fuel is in the tank? Unleaded fuel in a non-sealed system such as the crab does go off in a couple of months or so and I've read that it then causes the engine to run hotter - not sure if this is correct - but it would make starting harder.

David

Eventually the PCV arrived(!) and I've connected it up, to the manifold (removed that brass plug) and taken the other end of the PCV to the oil separator.  The car started up fine (as I'd wound the idle up to 700 rpm), but after about 2 minutes (wanted to let things warm up) it started shaking and the engine died.
I checked the dwell in that time - it was reading about 70 deg (should be 60) (not sure if that is affected by engine being cold - can't really see why?)
I have removed the manifold connection to the brake booster and connected  a vacuum gauge, was intending to tune the engine by vacuum.
I tried to loosen the clamp for the distributor - but the bolt is at such an awkward position I can seem to turn it more than 1/2  a flat.
Will have another go in the morning - charged the battery overnight and will inspect and clean the spark plugs.

Hi Dave - thanks for that.
I pulled out the oil cap and the engine kept running.  I tried a few times to put the cap back in but engine really grumbled. (I'll get a new cap tomorrow) I kept it  going for about 10 minutes after about 7min the thermostat opened.
There was a bit of black smoke in the exhaust - so I wound up the carby to lean it a  bit.
RPM was around 800.
Vacuum came up to 17-18 inch Hg.
A start.
Paddy

Hi Paddy

The good news is that with 20" vacuum the engine seems healthy. Without a vented oil filler cap the engine will stall. Did you try taking the cap off again when it stalled to confirm? It will normally run around 100 rpm faster when you remove the filler cap if the mixture is correct (or may stall if too weak).

A couple of other possibilities - check the exhaust for black smoke. If the carb float valve is sticking partly open it will flood and stumble as the engine warms up. Another possibility is that the coil is bad and breaking down as it heats up. Without a 'scope this is difficult to test, the best option is substitution. I would advise everyone to carry a spare so you may wish to consider this.

Setting the ignition timing as you describe may arrive at the right setting but sometimes these engines will have the highest idle speed up to 15 degrees over advanced. The critical thing with timing is the maximum advance - if this is exceeded engine damage will occur at high load / rpm. I would advise double checking the static timing reading that you now have.

I'm not sure which distributor you have as 0.40mm contact breaker gap would give 60 degrees dwell on a UK Mk11 engine with a 25D4 distributor (50 degrees with a 45D4 fitted to MK111 UK cars). A 10 degree difference would not cause your car's stumbling problem so we can revisit this later.

My advice now is to get the correct oil filler cap before chasing the rest of the fuelling and ignition possibilities and ensure you haven't ended up with an over advanced ignition. While you have the vacuum gauge attached check whether the vacuum falls as the engine warms up - before it stumbles.


David

Hi Paddy

Yes, the part number is GFE6003. It was used on a number of BMC /BL cars and vans. If you look at the pics here you can see the difference between a vented and non vented cap. MGB oil filler caps

Minis as far as I recall used both vented and non vented caps; the non vented cap is about twice the depth so easy to identify.

Sorry, I should have read your note closer where at point 3 you noted you took off the cap. The vented cap does indeed restrict the air flow considerably as the engine only needs to draw in enough air to extract the blow by fumes through the PCV valve into the inlet manifold without adversely affecting the air fuel mixture.

As the vacuum held that seems to rule out an exhaust blockage that occurs when hot and also borne out by the car driving OK.

With the oil filler cap off that could lead to the air fuel mixture becoming too weak and cause the engine to stumble, but I would have expected that to occur before 5 minutes when the engine was cooler - probably shortly after you pushed the choke in - I assume you pushed the choke in soon after starting with air temps of 23C?

That points to either the ignition coil failing as it heats up or fuel starvation excess as the likely cause.

Your car's problem appears to occur at idle and the car ran well but hot when you posted in mid January which suggests the coil was OK then but they are funny unpredictable things when they go wrong.


I suggest you repeat the test and when the engine stumbles check the plugs asap to get an indication of whether the stall is caused by a weak mixture / fuel starvation or from flooding (wet and black).

 Turn off the ignition and very carefully remove the float chamber cover to see if it has run low / out of fuel. You will need to disconnect the fuel pipe first and there will probably be some residual pressure in the pipe so take great car to catch the fuel and not let it spray on the hot exhaust. You could wait until the engine has cooled to be safe. If the float bowl is empty or very low check the float valve - the valves can stick shut - the fuel pump only delivers a low pressure. Also check to see if the float bowl is still clean.

Another possibility is that the float valve is not closing fully, usually due to some grit being trapped. This would result in the mixture being too rich and "choking" the engine as it warms up which sounds like your car's symptoms. In severe case the fuel leaks out of the float chamber overflow and the exhaust will emit black smoke.

Finally, did you have the bonnet open or closed when it stalled, if closed that could indicate vapour lock but it would be unusual after just 5 minutes of running.

Again, my advice to fit the correct oil filler cap asap as this will have a significant effect on the carb mixture and rpm settings.

Good luck

David

The topic was discussed here (and elsewhere).

oil filler caps

I suggest Paddy gets the original plastic vented cap with the inbuilt filter - at least until the problems are resolved. It seems as though the hole in the chrome cap is around 1.5mm.

David

After it stumbled, were you able to restart the car immediately?

David