Starts, then dies

[Nick Salmon]

It is a feature of several of my 7s that, from cold and with the choke knob fully out, they will start very smartly, run cleanly for perhaps 5 seconds, and then die away and stop. Operating the throttle makes it die immediately. Wait a couple of seconds, start up again, same thing. This will happen three or four times and then, at last, they will continue to run happily and everything is normal. Other 7s with the same setup will start and run immediately. 

I always manually pump fuel up to fill the float bowl prior to starting - which is what it initially runs on of course. All use 26VA Zenith carb.

Any clues as to why this happens? Is it a fuel pump issue?

[Martin Prior]

It is a feature of several of my 7s that, from cold and with the choke knob fully out, they will start very smartly, run cleanly for perhaps 5 seconds, and then die away and stop. Operating the throttle makes it die immediately. Wait a couple of seconds, start up again, same thing. This will happen three or four times and then, at last, they will continue to run happily and everything is normal. Other 7s with the same setup will start and run immediately. 

I always manually pump fuel up to fill the float bowl prior to starting - which is what it initially runs on of course. All use 26VA Zenith carb.

Any clues as to why this happens? Is it a fuel pump issue?

Like you, Nick, I always prime the carb before starting from cold, and then usually turn the engine over three of four revolutions on the handle with the ignition off.  The car then always starts on the first compression.

I only use full choke on my cars on very cold days.  75% choke is usually quite enough.  If I do use full choke, the car behaves as you've described does unless I very rapidly push the knob back in by about a quarter as soon as the engine starts to run.

[Nick Salmon]

Thanks Martin.

Unfortunately, if I reduce the choke a little immediately after the engine starts it will die just as quickly as if I had opened the throttle a bit.

On each car the choke is adjusted correctly so it is properly shut when the knob is pulled out.

[John Mason]

Nick. Have a look at the carb under the throttle butterfly is a small jet that allows air to pass through the carb when the butterfly is shut thus allowing air to enable combustion. To get to the jet you need to remove the small brass screw underneath the carb. Extremel care must be taken when removing this jet to prevent damage. Sometimes it is better to clean the jet without removing it

John Mason.

[Nick Lettington]

I have always found it odd that the 3/4 position is the best one for my cold engine, but there isn't a slot in the choke pull. It is fully out or almost all the way in, a bit more in than that or flush with the dash. I'm sure I'm not alone as I have seen plenty of clothes pegs to hold the choke just so. Start with two (needed to hold against the spring)... Once she's warm, remove one peg and the choke pull slowly slides in at about the right rate...

Does the lack of the 3/4 out position on the choke pull suggest that there is a problem with the old carburetor that wasn't the case when spangly and new?

[Thowdfella]

It is a feature of several of my 7s that, from cold and with the choke knob fully out, they will start very smartly, run cleanly for perhaps 5 seconds, and then die away and stop. Operating the throttle makes it die immediately. Wait a couple of seconds, start up again, same thing. This will happen three or four times and then, at last, they will continue to run happily and everything is normal. Other 7s with the same setup will start and run immediately. 

I always manually pump fuel up to fill the float bowl prior to starting - which is what it initially runs on of course. All use 26VA Zenith carb.

Any clues as to why this happens? Is it a fuel pump issue?

I  Had the identical problem a couple of weeks ago. As suggested the small equalising brass jet by throttle butterfly needs to be taken out and checked but my problem was behind that jet is a very small hole leading into the centre of the carb. Also, remove the slow running  and you will see another small hole at the top of the screw threads. Check that as well

[Nick Salmon]

I have checked the jets - including the little one underneath - on all the carbs and everything is clear. Agree that 3/4 choke is about right once running and that two clothes pegs is good a little later. But the choke has to be full out for the engine to catch. Anything less and it won't run from cold.

In discussing this do bear in mind this is three separate A7s displaying the same characteristic.

[JonE]

are they all used with fuel pumps, or are some running on gravity feed as a modified spec, out of interest?

[Nick Salmon]

All on mechanical pumps with rear fuel tanks.

[Reckless Rat]

Just trying to think outside the box... are your cars still on manual advance - retard distributors? Could this be a timing/ignition issue rather than a mixture one...

Final question - is the fuel stale?