Idle mixture adjustment, I guess it's screw in to weaken then mixture? Checking the axle bolts yesterday, I got a very dirty forearm from the soot on the exhaust, so it's running rich.

Cheers,Ben

Ben,
unleaded fuel tends to produce a 'sooty' exhaust, so the idea of being able to judge the mixture by looking at the exhaust tailpipe is a thing of the past.

In any case, the size of the idle jet and the setting of the idle mixture screw have no significant effect on the overall mixture beyond about 1/8 throttle opening.

It always amuses me when folk mention that they're tweaked the idle mixture screw and it made no difference to how the engine ran at full throttle.
To make any difference from 1/8 throttle upwards, you need to be changing fuel jets and/or air corrector jets...

ken

Ah, I've just been for a run and got the car nicely warmed. At idle I could see puffs of black smoke, so I wound the mixture screw in until the puffs diminished. This was accompanied by an increase in idle speed, so wound the screw out a little to reduce the speed. I'm still getting slight puffs, but not as bad as before.

Don't forget, I live in suburbia so the car spends most of its time in traffic jams and traffic lights. The car wouldnt start initially, so I popped some new plugs in. Here's the old ones:



Oh, and yes I see why that might be amusing, the clue is in the name of the adjuster after all!

Thanks, Ben

Ben,
did the car pass an MOT test recently, or is it old enough to be exempt from the emissions test apart from the 'visible smoke' part?

If it was tested and passed, it's odd that the idle mixture was so far out.
I always ask for the test to be carried out anyway on 'oldtimers', as the readings give quite a good idea of the engine's mechanical condition and state of tune.

ken.

Yep, it's exempt from emissions (at least, they weren't tested)! I think i wound the adjustment in by around 1.5 turns in all. Mechanically the engine should be top notch - new pistons, barrels, carb, breather and fuel pump. Of course, that says nothing about bearings etc. but the plugs are a good indicator of the state of tune. Next time I'm passing I'll get the gas analysed.

I have the same symptoms...nearly.
I have a 435 with a new carb from a source in Germany.
When I finally get the engine to start, it seems to run well on the above idle circuits. I increased the idle with the fast idle adjusting screw. I've tried to back off the fast idle screw while working the idle air screw and idle mixture, but can't keep it running. And then it just doesn't want to restart.
I started the idle mixture 2.5 turns out, and it really doesn't seem to have an effect when adjusting. I'm not sure where the idle air screw should start.
Float level is correct at 25mm with the float removed.
main jet is 155.
Emulsion tube (I think, visible inside the choke) is AC
The two brass jets on the outside (bypass jet and idling jet) are unmarked.
Just today I took all the jets out and blew everything out with air. Put it back together, and nothing changed.
Compression is adequate at 105 and 112.
Spark is within a tooth of the static mark.
I'm at my wit's end.
David

I had a problem also with a new carbie purchased, the idle circuit was incomplete. The carbie was never manufactured properly, it was fine when you drove but just stalled at idle. It took forever to work it out, only a knowledgeable citroen man with great patience found it

I went out and looked this morning, and there is a small drilling from the idle mixture cavity into the choke of the old carb. It's not there in the new one.
I cleaned up and blew out the old carb, installed all the brasswork, and installed it. With it, I seem to be able to start the engine, but can only keep it running by pumping the accelerator pump.
Does anyone want to make some money?
How much do you want to have me send my carb, put it on your 435, make it run, and send it back?

I'm sure I have a "Bitsa", That was established on a different topic.
The car came with a 425 engine that I've just shoved into a corner while I worked on the car and the 435 that was installed.
I'm starting to think that the 435 was installed on the 425 transmission by a previous owner. I think perhaps the PO had the same trouble I'm having, and gave up. I'm going to see what's up with the 425, and perhaps reinstall it.
David

David,
whereabouts are you?
I've recently sorted out a single choke carburettor for a 602 engine in a Mehari and posted it back to the owner...

My mehari and a great job by Ken!