Skoda Favorit Pierburg Puzzle

[RicardoM]

What about the ignition timing marks topic? Have you realized the rough idle has nothing to do with the timing and it is a vacuum leak?

[jms024]

Hi Ricardo. Timing looked good as also all the 'spark related' components which I could check. I still did not swap the high tension leads and ignition module though. However, lately I've noticed there was a small fuel leak from underneath the carburetor. This makes me think that there was actually a vacuum leak before which now has got worse enough to even let fuel pass out. 

 

Upon replacing the bottom steel and backalite plates the fuel leak problem even got worse! I've taken the plates to an engineer who will make sure the surface is 100% straight and then assemble everything using silicone rubber gaskets. I will also replace all vacuum hoses since they are looking a bit tired. As per diaphrams and so on I've tested them using a vacuum pump and they all seem to hold properly.

 

After all this I want to make sure the carb is set properly but since this is my first experience with a carb engine i'm not quite sure how to do it properly. 

[RicardoM]

http://www.mediafire.com/file/k8ve3sp0l9l0lac/Pierburg_2E3_by_masster.zip

[Breezy_Pete]

Power valve diaphragm?

[jms024]

You're the best Ricardo! I just picked up the plates from the engineer; I just didn't receive the silicone rubber sheets yet  :(. hopefully will get them done this weekend. Will keep you updated!

[cinedub]

Hi all!
As I'm out of ideas, i would be happy, if anyone could help me.
I have a pierburg 2e3 carb, on a Favorit 136 engine, from 1990. 
The engine runs fine, accelerates fine, and the idle is also good.
I have changed nearly everything on the carb,
-the accelerator pump
-the fuel enrichment valve
-the bottom and top cover seals
-vacum tubes
and i got rid of the ttv, and pdu, as they were faulty.
-choke works fine.

My only problem is that the car has a huge fuel consuption, like 15Liters/100Km.
My best was 8L but this was at a long trip with 70kph without a stop. 

Please help me, I don't want to spend my life at the petrol station.
Thanks in advance.

[RicardoM]

Tell us the history of your problem. This is often overlooked by most people asking for help. How did the problem start? What event do you suspect that contributed to it? Remember we are not wizards and every car is unique. You have full access to your car, you know all its history, we don't. 

[jms024]

So by today its been a couple of months since I've installed the carburator to the car after having the plates engineered and using silicone gaskets. After all this and a tune-up to the air/fuel mix, the car is running like a dream; very smooth and with a great fuel consumption figures. 

 

Thanks all those who helped especially @RicardoM for being very helpful and for your professional advises.

[cinedub]

The car was in a garage for about 5years, before that it worked fine. When i got the car, there was no idle, i couldnt even start the car. I have replaced the spark plugs, cleaned and set the carb, and changed what i have written in my previous request.Also replaced the filters and oil etc. set the valve gaps.... it has done over 4000km-s. Now it works fine but the fuel consuption is bad. Engine is in a good condition, no oil consuption or so. Its ticking over around 500rpm and accelerates to 100kph in 13secs. I dont know much about the fuel consuption before, they said it was around 8L avg.

[RicardoM]

9 hours ago, cinedub said:

Its ticking over around 500rpm

The idle speed should be 800 rpm.

 

Question: if you screw the mixture screw all the way in, does the engine stop?

[cinedub]

Yes, it's currently 1,5 turns open.

[RicardoM]

From my experience, a high fuel consumption is 95% due to vacuum leaks between carburetor and intake manifold. The rest of 5% is due to wrong setup of the carburetor, faulty parts, wrong parts, etc.

 

Note: I have counted only carburetor related issues. I didn't take into consideration fuel leaks, heavy loads, aggressive driving, sticky brakes, etc.

[cinedub]

The gasket between the carb,and the intake manifold is brand new, and i set the carb as written in the manual. it works fine, but eats my head.

[RicardoM]

8 hours ago, cinedub said:

The gasket between the carb,and the intake manifold is brand new

That is not a guarantee of flatness or tightness in our days. Anyways, I gave you my opinion. If you have already decided that everything you bought and did is OK without any second thought, you are left with one single choice: pay royally for petrol.

[cinedub]

So, I have disassembled and set the carb again, and checked everything, the engine still runs fine, but wont stops when i turn the mixture screw all the way in. the idle is set to 800 at 1,5turns on the mixture screw. It just lowers the idle, so it almost dies.

How should i check for leaks, and where? I have assembled the intake manifold-carb gasket with some gasket sealant and with the included cardboard gaskets. 

The current fuel consuption is 10L /100km using the car for 15km distances.

Thanks for any help in advance.

[RicardoM]

2 hours ago, cinedub said:

How should i check for leaks, and where?

There are two methods I am using:

1. the propane gas method
2. the smoke method

We are looking for any vacuum leaks between carburetor and intake manifold.

 

Method 1: use a propane gas bottle with a hose attached to it. Start the engine and let it idle. Open the valve of the propane bottle and slowly move the open end of the hose around the base of the carburetor. If the idle speed increases, you have found the leak.

 

Method 2: with engine stopped, involves filling the intake manifold with smoke using a pump. Cover all exits of the intake manifold. The pump can be a small air compressor for tires, a barbecue fan, a mattress foot pump or even a bicycle pump. There are many youtube videos showing that. Use a bright flashlight to look for smoke escaping.

[cinedub]

I can get a high power electronic cigarette with a big smoke, i will try it tomorrow.

[cinedub]

So, finally i had some time, i have checked the intake manifold for leaks, and there was no smoke coming from it. I have replaced the spring in the aftermarket part load enrichment valve /or whatever its called/, as in the original, the spring was much easier to press, and it was also smaller.  Idle is smooth at 800rpm. Shall i check the power brake vacum tube? Brakes are fine anyways.

[RicardoM]

1 hour ago, cinedub said:

Idle is smooth at 800rpm. Shall i check the power brake vacum tube? Brakes are fine anyways.

Most probably the enrichment valve had a ruptured diaphragm (shown in red in photo). Extra fuel was sucked almost all the time by the engine resulting in a high fuel consumption.

 

If the idle is smooth and the average fuel consumption is 7.5 l / 100 km or less, you're good.

Edited 8 October, 2017 by RicardoM

[cinedub]

I have only replaced the spring in it, (in the blue field behind the red line) the valve was replaced a year ago, i don't understand, what's ruptured?

[RicardoM]

You said you've changed only  the spring inside enrichment valve. With a spring from where? A stiffer spring will not allow the enrichment valve to close thus more fuel being sucked in both Venturi tubes. This raises the fuel consumption... Frankly I don't see how you have reduced the fuel consumption (if successful). As for the diaphragm part I will not add on it for now because it takes a lot of writing to explain. For somebody who knows in detail how this carburetor works, the logic of my assumption is self-evident.

[cinedub]

About a year ago, i have bought an aftermarket complete enrichment valve with the housing. I have looked inside it now, and compared the spring with the original one which i have taken off the carb. The spring is longer, and more stiff in the aftermarket one.

I will upload a picture tomorrow. I will find out soon if the economy got better or not.

[cinedub]

Hi again!

So i think, i have finally found something related to my problem:

Unfortunately i dont know, what causes this, but i think its not normal, as the idling fuel hole is at the bottom of the carb. This is the first stage of the carb, the second is dry, as it should be. I was told to check the accelerator pump, its new and i have also tried to change the little red thing inside it, with no luck.
(just to add something to my previous reply, i got a brand new enrichment valve, it's much better, than the previous, and i have also resurfaced all the sealing parts at the bottom of the carb, made new gaskets, etc)
Thanks for any help!

Edited 1 December, 2017 by cinedub

[RicardoM]

1 hour ago, cinedub said:

I was told to check the accelerator pump, its new and i have also tried to change the little red thing inside it, with no luck.

This kind of advice comes from somebody that has no idea how this carburetor works. Check this topic because I've uploaded two documents that help a lot if you read and understand them.

 

Now, about the video. Congratulations for it  I know it was difficult to record it in good light and focus. This is how everybody should post for a quick advice.

 

So, there are several things that give as clues about what is wrong.

1) Fuel dripping erratically into venturi tube. This tells us the level of fuel inside float chamber is disturbed. We say the carburetor is flooding.

2) The sound of the air flow. It is a crackling, random hiss denoting a turbulent flow. The sound should be a steady hiss at idle.

 

Both clues indicate a vacuum leak. The carburetor on Favorit and Felicia is super-sensitive on vacuum leaks. By the way, when you say "I made new gaskets" what do you mean? You made them of what?

Edited 1 December, 2017 by RicardoM

[cinedub]

I made new gaskets from 2mm cardboard, and assembled everything with silicone gasket maker. I think, it's not fuel resistant, but it's the best i can get at the shops. I have used it for assembling engines, it has done it's job every time. I dont know, where the vacuum could get in, i dont have pdu, ttv, the plastic spacer and the metal thing has equal thickness, I have absolutely no idea, where the vacuum leak could be.