Weber DFEV carb vacuum signal at idle.

[VDub Campers Ltd]

So. I’m currently jetting as per that infamous article https://www.aircooled.net/making-weber-progressive-dfev-work-aircooled-vw-engine/
Which i always thought was horseshit in terms of jetting.
Prim idle 50
Sec idle 65
Prim main 160
Prim air 180
Sec main 180
Sec air 180

Ran like crap. Spark plugs sooted up.
Spark plugs don’t lie.
This is why I’m doing this. There are articles like that one and advice like the power valve removal. In my extensive testing it’s not bearing fruit. This thread is kind of about proving that.

I’m now gonna rejet to what I think is best, and then test for faults.
I’ll run leak down test, and look for spark misfires.
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Pics of current work at our google profile:
search VW Engineering Ltd on Google.

[Wildthings]

Wonder if you are experiencing a dropped valve seat or something? These engines are pretty notorious for the valve seats working loose and at some point the seat gets cocked and the valve no longer comes close to sealing.

We went through this maybe 8 years ago, we were getting ready to do our spring migration from Arizona to Oregon and I told my wife I didn't know what was happening to the engine, but I thought we would be lucky if it made it the 1100 miles home. Made it home fine, but the next day the wife took it to town to do some shopping and she said it barely made it up the hill coming home. Spun the engine over by hand and it was obvious one cylinder had zero compression any more and removal of the head showed an intake seat had dropped.

[W1K1]

does the manifold have heat risers that work?
John emphasized that lots of manifold heat was a must in that tuning article.

You really have to jet for what the engine wants/needs, there are so many variables, elevation, compression, spark, timing, fuel, etc.
That's why I bought the LM-2 to help narrow down what jetting it needs, and where/when

[SGKent]

there can be several reasons plugs soot up including choosing the wrong gasket in the carb rebuild kit. Some have holes in places others do not. It all depends on what was originally designed there. I had an Opel GT with the power valve and I used the wrong gasket because the correct one was not in the kit and I did not catch it. It ran awful. Finally figured it out and put the old gasket back in and it ran fine.

A bad capacitor / condenser can cause it to run rough and soot up. So can a bad float adjustment.
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“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[Wildthings]

[mikedjames]

I have not yet wired the ECU but I remembered I have a mechanical gauge.

This is ported vacuum .. first Throttle cracked open on cold idle cam.

Then Throttle at 850 rpm warm idle, off the idle cam.

I pulled the hose the gauge read the same just to the left of zero when open to air.
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Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[pharos]

[mikedjames]

With or without the power valve, that primary main is big for a smaller engine.
1641 DP in a bus
Prim idle 45
Sec idle 65
Prim main 125
Sec main 140
Prim air 165
Sec air 180
Prim emulsion F66
Sec emulsion F50 (another pair of holes further down)

This has been set up with a permanent installed AFR meter and driven.

Disabled power valve. 30C Hot air feed into air cleaner, heat risers sort of working.

SVDA distributor.

It needs power to the choke wire so it comes off the choke and starts running normally after a few minutes.
If the choke is still on, you get vacuum from ported vacuum at idle and an increasingly high idle with the throttle end stop controlled by the cold idle screw behind the choke mechanism. (as my picture of the gauge connected to the distributor advance hose shows).

The idea is that the cold idle screw rests on the stepped cam behind the choke capsule (small brother to the 34PICT-3 ).
That cam rotates with the choke and drops the throttle down to the normal hot idle position after a few minutes.
_________________
Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[pharos]

[Wildthings]

[VDub Campers Ltd]

Thought I’d clock back in and report what happened in the end.
After spending numerous days on this issue, I advised the customer to replace this DFEV carb, with a pair of Weber ICT’S. (budget constraints) I told the customer that I was confident his engine was not at fault, but that carb model was the issue. I offered him money back guarantee that I could install a pair of ICTs on there and I could have them installed, setup and tuned within 6-7 hrs, and they would work correctly with his Bosch 034 vacuum advance distributor, and he would be satisfied. He took my advice. They worked immediately. Engine was faultless.
I am convinced that this carburettor cannot work correctly with a vacuum advance distributor. However, MikeDJames (above) has appeared to have demonstrated that his engine does idle at a satisfactory speed, without a ported vacuum signal that advances the timing at idle. So I’m none the wiser for my troubles.
As I said in the beginning. I have test driven vehicles with these carbs, and they have been pretty good. But I can’t remember if those vehicles I drove had 009 dizzys with no vacuum advance function. Hence no issues as per my original comments highlight.
I will not ever bother with attempting to solve this mystery again. I didn’t charge my customer for the days of hrs I put in trying to solve this for my own curiosity & sanity. I consider myself experienced and competent although I’m certainly not infallible. But if I cannot make two of these carbs work on an engine after 4 days of experimenting and testing, then I have to say, I’m done with those carbs. I’ll never attempt to make one work again 😄
_________________
Pics of current work at our google profile:
search VW Engineering Ltd on Google.

[mikedjames]

I have always used full stock hot air off a 34PICT-3 through the oil bath air cleaner., fed into the top of my progressive via an air box on top of the carburettor.

The mixture screw is where 14.7 AFR is at 850 rpm idle appears.. maybe 2 , maybe 3 turns out.

Whenever I had lean running (pinging) that was the power valve staying shut because the engine was not running fast enough at WOT.. sometimes I could waggle the gas pedal and get it to settle on a different AFR ...

I like having a working choke - the ease with which my bus started at a recent campout compared with those Weber duals and 4 barrel Dellorto carburettors on a cold damp morning gave me pleasure..
_________________
Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[mikedjames]