1200 Herald B30 PSE1 Carburettor running rough

[Ty_bach]

Up to this week, the car has been running smoothly. Then suddenly overnight, I start the car next day and it will fire up , but won't keep going. the revs rise and fall very roughly with the choke either in or out and eventually it dies and you start over again. The engine starts easily but will not keep running for more than 30secs - one minute.  Because of the easy starting, I am assuming its carburation. I noticed petrol was weeping from the accelerator pump so decided to replace the diaphragm, but that did not fix the problem. I have thought about water in the petrol but since it has been sitting in my garage for a couple of weeks and not been in the rain, this has been discounted. I have had all the jets out and checked. Still no improvement. Now running out of ideas.

[Colin Lindsay]

Possibly flooding or running very rich? Have you checked the plugs? If the carb is flooding the engine will start easily enough and will run until it floods past the point of no return, then it stalls, and won't start again until the petrol drains back or evaporates away. Have a look at the float valve, clean or replace as necessary? Keep posting as you try solutions, or think of other things.

[Pete Lewis]

so you have cleaned the slow running jet  ??  

i would look at a low fuel level due to debris clogging the back of the float needle valve 

and then look at pump output ,  

Pete

[NonMember]

As well as Colin's flooding issue, it's possible to get the "starts well but then dies" if the fuel pipes are blocked - more likely after the pump, as Pete said. The residual pump pressure can re-fill the float chamber between starts but it can't pump fast enough to keep up with the engine's demand.

[Ty_bach]

Thank you all for your hints and comments. Having gone through them, I did discover that the needle valve on the float chamber was stuck in. I unstuck it and made sure passages were clear and the needle valve worked smoothly. I reassembled everything and started the engine again. Good start but  a few seconds later, it ran like a tractor or even worse and then died again, I was now getting suspicious that it was nothing to do with the carb but perhaps the ignition system. One of the weak links in the conventional ignition system is the condenser. So I decided to change it for a spare I always carry with me in the boot of the car. Bingo! the car started and ran normally. I took it for quick run round the block and it performed quite normally. 

Fiddling with the carb was not a complete waste of time since I took the opportunity to clean out the float chamber and check all the jets were free of dirt.

Thanks again for your help.

[Pete Lewis]

cheap fix   like it 

old diagnosis of condenser is it will normally idle ok but misfires and back fires when you try to rev it

not as yours 

have to say there have been some really useless condensers sold over the past few years 

many have very little inside 

Pete