2 hours ago, cinedub said:

I have absolutely no idea, where the vacuum leak could be.

There are many methods to find exactly where the vacuum leak is. Have you tried any?

Yes, i have tried the smoke method, the smoke only came out at the top of the carb.

 

3 hours ago, cinedub said:

...the smoke only came out at the top of the carb

The top of the carb had to be covered with a rubber/silicon glove for the smoke test to mean something. You have to build enough air&smoke pressure in the intake manifold to simulate idle condition. We're talking roughly 0.7 bar.

See video below as an example.

 

Alternatively you can use a propane torch to pinpoint tiny leaks (see the video below at 6:25).

 

On the video, the leak is in the brake booster. I am not sure, that mine is perfect, the hose is still the original one. I will try the propane gas torch at the bottom of the carb, and remove the brake booster hose for a while.

3 hours ago, cinedub said:

...and remove the brake booster hose for a while

Forget about it. The engine will not start.

...and close its hole on the intake manifold.

 

No reaction to propane gas, around the base, if i suck the booster, it's not holdig the vacuum but no changes are noticable with closed hole.

21 minutes ago, cinedub said:

if i suck the booster...

 

25 minutes ago, cinedub said:

...it's not holdig the vacuum but no changes are noticable with closed hole.

 

What country are you from?

@cinedub - I've made cardboard gaskets before. Could you post a photo of the cardboard you used, and tell us what tools you used to cut the holes in the card please?

I am from Hungary, and here everybody hates this carb :D.  
By the way, i have a Skoda120L with a favorit engine in it with the pierburg carb now, but
I'm looking forward to buy a BMM injection system from a felicia, for a bargain.
I don't have the choke installed on the pierburg, so the coldstarts are getting harder in the freeze nowadays. 
But until i have time to take it out from the felicia, and install the system to my car, I would really like to reduce the fuel consuption on the pierburg just a little bit, i would be happy with even 9L/100km.

1 hour ago, KenONeill said:

@cinedub - I've made cardboard gaskets before. Could you post a photo of the cardboard you used, and tell us what tools you used to cut the holes in the card please?

Yes, i will post some in the evening.

10 hours ago, KenONeill said:

@cinedub - I've made cardboard gaskets before. Could you post a photo of the cardboard you used, and tell us what tools you used to cut the holes in the card please?

I have used a bigger pair of scissors to cut a rectangle shaped piece from the big cardboard first.
The cardboard is from a bigger notebook, with a hard cover.

Edited 4 December, 20178 yr by cinedub

10 hours ago, KenONeill said:

@cinedub - I've made cardboard gaskets before. Could you post a photo of the cardboard you used, and tell us what tools you used to cut the holes in the card please?

In case of Felicia, It's not how you make the gaskets, it's the material you use. I've tested in the past all kind of materials. Ideally the gaskets should be made of 1 mm Viton rubber which is both temperature and petrol resistant. Since I couldn't get my hands on small pieces (vendors sell only 10m long x 1m wide rolls for $1,000 )  I found out that the best sealant is REINZOSIL, a "liquid" gasket temperature and petrol resistant. Apply a continuous 2mm string of sealant, not smeared. Torque evenly at 8 Nm, not more. Let it cure for a day before starting the engine.

@cinedub @RicardoM Well, I'd use that sort of toolkit for cutting gaskets. However I agree with Ricardo that you absolutely must use a fuel-proof material for making carburetor gaskets, and that sort of plain card is not fuel-proof.

 

Where the gasket is not in permanent contact with the fuel (eg a float chamber cover) you can use ordinary card after treating it with a fuel proofer (no brand name recommendation, but you'll probably find it in shops selling internal combustion remote control engines and models).

Hi again!
So finally i have found the problem, I think. I have installed a Bosch Mono Motronic Felicia injection system, since, but had troubles with it, so started to found out what's wrong with it.
The manifold on the cylinder head side was curved. I haven't installed it back, but i'm sure it was leaking, even with a new gasket. It was absolutely not straight, but enough to run nice with the carb. 
Since i have installed an external AC, and changed the diameter of the fuel hoses, i'm not sure i will put the carb back on for a check, but as i have spent a lot of money on it, i think i will try it one day, just for fun.

If anyone has issues like me, (car runs fine, only economy bad, check it out, and make it flat as you do the aftermarket carb-manifold gaskets!

If this wasn't the problem, then idk

Cheers!