Motor stalling issues

[Doob]

Regarding our 1971 low light Kombi – Stock standard dual port1600cc AD code motor with original single Solex 34 PICT-3 (flange No 299-2) carburettor and a Bosche 0231 167 049 / VW 113 905 205 AJ (DVDA) distributor. It has standard power assisted front discs brakes (i.e. brake servo unit with vacuum line from intake manifold).
Since having the carburettor & distributor rebuilt by ‘1500king’, the Kombi is much more drivable. Once it reaches operating temperature, the motor will idle at 900rpm purring like a kitten, while the vehicle is stationary.
However, I still have an issue with the motor stalling on occasions.  When decelerating & braking (e.g. approaching stop lights), I depress the clutch pedal to change down gears and also before coming to a full halt, the motor will run very rough and often stall.  There is no problem starting the motor immediately after a stall, and it will then idle perfectly, as before.
It seems there is something about the braking & decelerating motion that upsets the motor.  I am guessing it is a fuel issue, but I am not sure.  Possibly an air leak issue with the brake servo system but it all looks OK.  Applying the brakes while the vehicle is stationary does not seem to stall the motor.  Possibly a lean fuel mixture when the foot is off the accelerator pedal and using the motor to slow the vehicle?  Just not sure.
This is an intermittent problem – but on my last run it was frustrating and embarrassingly frequent.
I thought I had read about someone else with a similar issue on this forum, but I cannot find the post now!
Any suggestions & words of wisdom would be greatly appreciated.

[Tintop]

Anytime I get that symptom (usually accompanied by little pops from the exhaust on a long downhill with no accelerator) it's time to blow through the idle jets (and test that the solenoids are working)

Only usually happens if the hoses or carbies have been off recently

[Doob]

Anytime I get that symptom (usually accompanied by little pops from the exhaust on a long downhill with no accelerator) it's time to blow through the idle jets (and test that the solenoids are working)

Only usually happens if the hoses or carbies have been off recently

Many thanks Tintop.
Not experiencing any exhaust poping, and I think the carby solenoids are working OK (but will double check) 
The fact that it idles perfectly when the vehicle is stationary - and performs reliably under power - made me suspect that carby jets were OK .
But yes - a carby clean & inspection is on the To-Do-List !
Cheers
Grant

[Melissa]

I was having very similar problems cutting out when coming to a roundabout or lights but mine was in Josie which is an auto. Getting the carbies rebuilt and a new distributor has fixed the issue.

[Wayne Murray]

When you are at a set of lights, does putting the foot on and off the brake pedal make it run slightly rough. I had an issue similar to what I mentioned and one day looking for the problem I had the car running and pressed the brake pedal and the motor stopped. The brake booster completely failed. I think in my case my booster had a small hole in diaphramit gave likely at home.

[Oldman]

Also worth checking the fuel filter………

[Doob]

This KCA forum is great !

Thanks Malissa - I have had the carburettor & distributor rebuilt by 1500king (VolksDoktor in Adelaide). It has made a big difference to the drivability of the vehicle. But I may need to contact  Andrew again and see if he has any suggestions on this stalling issue.

Thanks Wayne. - The brake servo / booster & hose would be one of the prime suspects. But when the vehicle is stationary, applying the brakes does not create the rough running and stalling that I get on deacceleration. I am sure the  brake servo / booster has not complexly failed as I am still getting power assist when applying the brake pedal.
One option is to isolate the booster by disconnect the vacuum hose from the intake manifold - plug the manifold port - and carefully test it on a quiet street where reduced braking efficiency is not too risky. 
 
Thanks Oldman.
The rough running & stalling certainly feels like it is starving for fuel (or incorrect fuel & air ratio) 
I will check again, but the fuel filter looks fine (no obvious residue and I can see the fuel bubbling through). And there are no issues with acceleration and cruising at highway speed for extended periods. The motor idles nicely when stationary. It is only when I disengage the clutch while deaccelerating that I am having issues.

Many thanks.
Cheers,
Grant

[Oldman]

Also worth checking the one way valve, inline in the vacuum hose, to the booster……usually located in the engine bay close to the inlet manifold.
It should only allow pressure in one direction……towards the manifold. It has an arrow on it to indicate correct orientation. Easy to check…..disconnect, and suck…..it should hold without leaking down.

[Oldman]

Something else…….
I know you have had the carb rebuilt, but it would be worth checking the O ring on the air volume screw…..the larger of the two on the side of the carb. 
I had exactly this issue with my son’s ‘71 and the O ring was cracked/incomplete……replaced it and no more stalling on idle.
Just a thought.