The 'choke' on a diesel motor ...

[dekhelia]

... so what does it actually do? (I realise it's not a 'choke' in the classic sense, of restricting air and increasing fuel.)

The reason I ask is that I've been led to believe from various sources that it advances the timing somewhat: but I've just adjusted the position of the injection pump on my AAZ, and gone too far - it's clattery as hell, smoky, not much grunt, etc & etc. So it needs to be backed off, obnviously, and I've decided that I'm going to invest thirty-odd quid in a dial gauge and adapter from a German company.

But in the meantime, pulling out the 'choke' smooths the engine out considerably, and seems to ameliorate the effects of having the timing too far advanced.

So what is it that the 'choke' actually does - anyone know?

[Oldiebut goodie]

It advances the pump timing - sounds like you are retarded!

[Oldiebut goodie]

[dekhelia]

Thanks for the pics and info, OBG. Definitely not retarded, though - pump has been moved anticlockwise (looking from rear of van) so that its top gets closer to the engine.

This is advancing the timing ... right?

[Oldiebut goodie]

Yes, if everything is locked off.
I can't see how it is improved by advancing though if you advanced it from a normal running state. Why have you "adjusted" it to start with - especially without the dial gauge?

[dekhelia]

Why have you "adjusted" it to start with - especially without the dial gauge?

Long story short is that the pump had to come off and go for repair. Even with everything locked off when reinstalling, it's still only a rough position - hence the need for a dial gauge. Until I get one, I was experimenting with what happens at different advance and retard positions.

I've never been happy with the way the engine runs. Yesterday, even though the pump was clearly too far advanced, the low-rev running was incredibly smooth and quiet compared to what I've known.

As I understand it, too much advance or retard won't actually damage anything.