What's the Elec Connection on the PIC3 Carb?

[jeremy]

I was having a look at the carb on my 33 - trying to find the source of the flat spot on pull away. I think I've eliminated a vacuum leak so it was back to traditional carb faults. I noticed a screw in thing with an electrical connection from the ignition feed that's not mentioned in the Autobooks manual. Anyone know what it does? The carb is identified as Solex 34 PICS 3.
Ta,
Jeremy.

[Richard DAF Webmeister]

Aha. We have often discussed this, mainly due to the problems I had with mine!
It's a capacitor/solenoid thing that connects to the coil. We think that it was to help the engines meet emission regs.

But, it is crucial to ensure that it is firmly screwed into the carb - mine had a habit of working loose. And likewise must be a good electrical connection.

If not, you will find the that engine will run rough, and stall at junctions/lights, giving all the symptons of the tuning being out.

I'm sure that someone who really understands what it does will explain further, but hope this helps.

R

[spunkymonkey]

That's your electrically operated pilot jet, otherwise known as an idle shut-off valve.

The bit you can see is the solenoid, which is permanently energised (valve open) while the ignition is on. When you turn the ignition off, it de-energises and cuts the fuel flow to the idle jet to make sure the engine can't run on.

Was also fitted to the PICS40 -5 and -6 carbs on 44s, but not the earlier PICS34-2 which the Autodata book seems to spend all its time on (maybe he only had a 34-2 to strip as he wrote it??? )


edited to add: As Richard mentioned, it's part of the emmisssion control system. Well, more precisely, it's to counter the fact that the emmission control measures have a nsaty habit of creating hotspots and causing run-on. Rather than ditching the (not very effective) measures, they just add extra stuff to shut the fuel off.

Yep, the Green Brigade had a lot to answer for, even back then ;D

[jeremy]

That makes sense; thanks guys,
Jeremy.

[daf44]

hi there.

there was a similar system on the old beetle carbs that used to cause no end of trouble.

when the solenoid was unscrewed there was a 1 inch needle that was moved in/out to block/allow petrol to flow.

while it is not exactly recomended, cutting off the needle was very effective in curing the problem.
this did not cause any problems on the beetles but i don't know whether it would affect anything on the DAF.

someone else may know more.

paul44

[starider]

Hi, I suggest you leave the soleniod jet in place,just make sure it's screwed in properly and that it "clicks"when you turn on the ignition on,the engine will not tick-over if it's either loose or not working.As someone correctly said it was fitted as part of an attempt to reduce emmissions.My Dealership had, at the time these "emmission improvements" were made:to purchase one of the first exhaust gas analysers to check emmissions.There was a small diameter pipe on the silencer to connect the analyser to, and the various checks and adjustments were then made.Checks were made; and from memory these checks and adjustments made so little difference they were abandonded as part of servicing,infact the small pipe disappeared from the later silencers. The reason for fitting this "electro-magnetic jet" was to reduce emmissions at start and tick-over!!! I'm sure this doesn't help, but I enjoy a bit of a rant. Regards to all. starider.

[spunkymonkey]

Been checking back through some of my "period" tech literature and, as far as I can see, the main "emission control" measure on most cars of this era was severely retarding the idle ignition timing. That cuts NOX and hydrocarbon emissions at the expense of a big increase in CO2 due to higher fuel consumption. This was the age of mainly acid rain and smog concerns and global warming wasn't an issue - funny how the experts change their minds over time! It also suggests why an early gas analyser, measuring CO levels, wouldn't have shown much benefit.

Another effect of drastically late timing is much more heating of the cylinder walls and valves. Hence an increased risk of hot-spots and running on, countered by adding a cut-off valve. Probably the first symptom of ever-increasing complexity for ever-diminishing gains that's lead to modern cars and "technician" who can't diagnose without a computer.

Minor rant on eco-driven engineering over ;D