No start!

[John Cornforth]

Hi

There is also the remote possibility that the exhaust system is partially blocked, which will build up back pressure.

[Colin Wilks]

The symptoms you describe also fit with a condenser failing under stress, but then starting to work again after a bit of a lie down.

See Parazine's entry in the recent thread about testing condensers "I guess that the capacitor was breaking down under voltage stress, becoming progressively short or open circuit after a few minutes running. After not being used for a bit, it "healed" and became operational again."

[Duncan Grimmond]

Well worn distributors can behave like this. Do you have access to a spare or could you borrow a known reliable one?

[andrew34ruby]

Hi

There is also the remote possibility that the exhaust system is partially blocked, which will build up back pressure.

The symptoms for a blocked exhaust are generally that it will start and tick over all day, but not rev much.

---

its definitely compression, the engine will just suddenly run worse, refuse to rev and cut out over a couple of seconds.

Try dribbling petrol into the air intake during that couple of seconds. It sounds like a shortage of petrol, so might be worth feeding the carb from a bottle hung above, to eliminate the tank, pipe and pump.

[12jslater]

I've tried two new condensers, one is a know good one from my Morris 8 that I sold not a week ago, so that's definitely good, and the distributor is very unworn, it's in marvelous condition, even if it was worn surely that wouldn't cause the engine to start sweet as a nut but then die off?

[Malcolm Parker]

My experience would point to the distributor.  I have fitted 'good' unworn distributors with new points and condenser and had problems.  It is not unusual for there to be an electrical short within the distributor, often around the little post that the points pivot on.  I would try another distributor.

[12jslater]

I doubt it's a short as I have a nice fat blue spark both before the engine runs and after it dies, jumps maybe a 3/8 gap from the end of an ht lead to the block.

[John Mason]

Have you tried disconnecting the fuel pipe to the carb and plugging the end to stop leaks then fit a small say 1/2 pint of petrol temporary take to the carb and see if it will run for longer. If this works you know it’s a fuel problem but further back down the line from the carb. If it is no better at least you know the pump is ok. You say you get a good spark from the plugs so it appears the ignition is ok. That only leaves fuel and if you have done the test I have already suggested the carb OR a mechanical problem but you seem convinced compression is there which suggest valves and rings are ok. My bet is it’s a fuel problem not enough or too much. You say your plugs are wet so that’s makes me think too much.
If I was you I would start afresh and re check everything I have done we are all prone to sometimes missing the obvious.

John Mason.

[Bob Olive]

Hi

There is also the remote possibility that the exhaust system is partially blocked, which will build up back pressure.

I'm with John on this - it sounds like the exhaust might, somehow, have become (completely?) blocked, and I base that upon a very embarrassing identical fault wherein I checked everything but the exhaust... Worth checking I'd say.

[Eddamoo]

Im very much of the ECU and code-analysis DIY generation so problems like this really intrigue me!

If the exhaust is blocked, it should be pretty apparent on the restart as the car should struggle to even crank with the increased back pressure, shouldn't it?  10 seconds is a lot of gas volume so id be doubtful it would take that long for the engine to cut out.  Should be easy to see with a lack of visible vapour and exhaust pressure on startup?

• Doesnt sound like a lack of fuel issue if it corrects after 30min.  To rule it out, try restarting it on carb cleaner.
  
• Have you checked the bores immediately after it cuts out to see if there's any excessive fuel smell?  Maybe its flooding.
  
• Do you manually set the timing before each startup?  Is the timing slipping from a loose dizzy?
  
• You see a blue spark after, but it doesn't necessarily mean it can maintain it. Does the spark maintain its intensity after a long period of cranking for all 4 plugs?  Maybe the Coil is weak.
  
• As others have said, the condenser/capacitor could be bad and this is only exhibited after it is used for a period.