2E3 Carb - rough at part throttle cruise

[T25Convert]

Could do with some thoughts on this one.

When at a cruising speed (especially around 50mph) the van runs a bit rough - not terrible, just a little wheezy. I also get overly good MPG at the moment, and its a bit warmer than I'd like at cruising speed, which all suggests lean running to me.

If you give it some right foot, its lovely and smooth as the accelerator pump kicks in. It pulls well in all gears. Above around 60mph the issue seems to improve a lot. the more I cruise, the worse it gets. If I aggressively engine brake (working down the gears hard) it improves for a little while.

From this, I think that the main jet is a little blocked, so that with just it working its a bit lean, until around 60mph when I get full enrichment valve action. The engine braking develops high carb vacuum, which then sucks dirt out, hence temporary improvement.

I have a brickwerks rebuild kit on the way, just after thoughts on whats happening and whether ^^^^ seems about right.....

[kevtherev]

When you say rough does that include lurching and like misfiring?

[T25Convert]

Not that bad.

It' starts to hesitate a bit, and power drops off a bit. sometimes it surges a little, like it picks up a bit then dies back a bit again.

[kevtherev]

If it was me I'd be checking my float height, and if the stopcock is not leaking firstly.

[trundletruc]

I had a similar problem and it annoyed me for ages. I think the solution was that the interconnection between the primary venturi and the secondary venturi had worn and this meant that the secondary throttle was open when it should have been closed. In other words - when the engine should have been running on the primary throttle only, there was some air leaking in from the secondary throttle. This is often masked at idling speed by the mixture adjustment set to compensate.
So I would check the mechanism that stops the secondary throttle opening and adjust the metal prongs so that the secondary throttle can't hardly open when the primary throttle is closed.
There is no mention of this adjustment in any of the VW manuals I have read and only found out in an article on the internet to do with Ford cars that also had a variation of the Pierburg. I think there is a video on You Tube, in a foreign language that shows it. Try it and see if it makes any difference?

[CJH]

I did find a really useful manual that includes that adjustment - you can download it by clicking on the cover page below.



That particular adjustment is in section 5.

[trundletruc]

Thanks CJH that is a really useful document, very thorough, and a lot better than manuals twice the length.

[T25Convert]

Thanks all for advice.

Rebuilt carb, didn't adjust anything, just to see what effect a good clean and new rubber bits would have.

Slight error when I forgot to reconnect the fuel pipe back on, and squirted fuel everywhere, which promptly ignited for reasons unknown - no obvious source of ignition. Panicked few minutes whilst I extinguished it. No real harm done, might just have shaved a few years off my life!!

Now runs much much better, but now I understand how it works I'm getting a slight hesitation when the second barrel should be opening, so I think it's coming in fractionally too late. Will pop it off and check the gaps.