Pierburg secondary choke check?

[waltraud]

Hi, have got my Pierburg fitted to dg and timed correctly etc. Starts and runs fine but still boggs down on quick acceleration for about a second or possibly two then picks up and goes well. I have just repaced accelerator pump hopefully correctly and was wondering if there is anything that could 'hold up' or delay the second choke kicking in properly? I will also check that the main choke is shutting off correctly after warm up as i suppose if it got stuck on it might also be over rich or something...? thanks.
Seems like a good carb really, just they are old and been fiddled with....by the others not me of course?!.

[kevtherev]

The second coke is opened by the choke pull down unit, Its only job in life is to open the choke flap when starting from cold. If it isn't doing this, or not doing it enough, your carb will struggle to make the engine run smoothly within the first minute or so from a cold start, as the engine will not get enough air for the amount of fuel going in.

You can test it with ignition off, engine not running.

Firstly remove the whole airbox to reveal the carburettor.
The hose coming off the pull down unit is a vacuum hose
pull it off and attach a suitable hose to suck through it.



Then the harder you suck the more this flap opens
Crucially, you should also find that if you stop sucking, and stick your tongue over the end of the hose, it should stay in that position. If it gradually closes up again...your pulldown unit has a leaky diaphragm, and really needs replacing. This is a common failure, I believe.
these are obsolete from VW
A further test can be done, Start the engine and allow it to idle
You should be able to close the gap until the last 3mm.
the ability to close it easily suggests a problem with the unit

If it holds it's position it may need adjusting of which the procedure is on page 4A*11 of the haynes along with the procedure and gap value
there is an adjusting screw as shown here



hope this helps

[waltraud]

Cheers kev, very helpful, i shall have a look tomorrow pm and should then have at least ruled in or out a few possibilities. My other thought was acc pump but seems less likely. Will let u know how she goes. thanks, much more useful than my other idea which was to spend money i don't have on an ebay refurbed pierburg......... Tim

[kevtherev]

I would also be checking for any air leaks.
Carb manifold gasket
Brake servo vacuum hose.
all the vacuum pipework.

The accelerator pump is adjustable too..

[waltraud]

Dear Kev/all,

I have tested the pull down unit by attaching a hose to it while engine off. The choke 'plate?' moves to a maximum of about 5mm away from side of barrel and then if i put my tongue over the end of the tube it returns to its original position, not immediately but within a second or two. When running and idling from cold the choke flap is slightly open and although there is slight resistance to being pushed by my finger i am able to fairly easily close it. Sounds like its worn.........do you know where i might find a replacement or is it only s/h. I still can't quite work out why this would effect the trouble with progressing to midrange. I.e. she will start and idle and then when warmed up seem to run fine but get bogged down, does this choke pull down unit issue also effect that?
thanks v much, Tim