17 minutes ago, nta16 said:

Are you sure the warm air is getting to the carb, or that icing is the problem.  Even if the air is warmed there can be too much humidity.  Are you starting the car in a garage with mats or old carpeting on the floor or lots of cloths, clothing, anything that holds a lot of damp.

The whole air intake system was warm, even the round air filter cover that sits directly on top of the carb. I have started the car outside and inside the garage. I tried blocking the first pipe with an old shirt but the shirt was dry and I've also tried to redirect the first pipe to end near the exhaust manifold as well, neither of which worked.

17 minutes ago, nta16 said:

As an experiment you could try heating the petrol in the tank and perhaps temporarily insulate the fuel line so it arrives at the carb above air temperature as the fuel delivery of the carbs cools the petrol, obvious take care how you heat a petrol tank.  As a second stage of the experiment you could then move on to insulating or warming the carb again obvious take care with something that  is putting petrol out.  Or you could pre-heat items before trying to start the car.

 

Once the car is started the heat build up from the engine should also help with warming the carb but icing can still happen.

 

More details are required, what is happening when, details from starting the car, what situation the car is in, what happens after start, how long after start, and so on.

The engine is very warm and melts the ice in a few minutes once it forms. The ice forms in about 15 min of driving, the revs can be kept below 3k, doesn't matter. First, the idle drops, when pressing the clutch in or just taking it out of gear and the engine stalls. For a bit, the revs can be held higher by pressing the accelerator but eventually, the accelerator stops working. Press it as much as you want, nothing happens, then it dies and I have to wait a few minutes before the pedal works again and the engine doesn't stall. Right before it dies fully, the pedal usually cuts in for a few seconds but then stops responding till the ice is melted. 

17 minutes ago, nta16 said:

And yes I saw you put "It idles well now and also passed emissions with 0.2.. % CO" which shows that passing a test does not mean the car goes as well as it could or should, it is the same when somebody says that the car passed an annual MoT test.

 

The car works well, the idle is good, doesn't move up and down and the acceleration is fine.

Edited 7 February, 20251 yr by RalfRannet

22 hours ago, RalfRannet said:

The whole air intake system was warm, even the round air filter cover that sits directly on top of the carb.

How warm is this and how long did it take to get this warm?

 

 

22 hours ago, RalfRannet said:

The engine is very warm and melts the ice in a few minutes once it forms. The ice forms in about 15 min of driving, the revs can be kept below 3k, doesn't matter.

This is more detailed information than I have noticed before. sounds like you might be running the carb over rich for fuel.  Have you noticed the colour of what comes out of the exhaust tail pipe when or just before this happens in your rear view mirror?  Are you sure the automatic choke flap is fully open at these times?

 

 

22 hours ago, RalfRannet said:

The car works well, the idle is good, doesn't move up and down and the acceleration is fine.

No it is not the carb ices up, the idle make seem good but that is perhaps an assumption on your part, what checks have you made to confirm this?  The acceleration from idle may be fine but it's not after 15 minutes of driving.  You may be setting up with the idle but you do not drive the car at idle.  A fuel mixture that is rich can sound and feel better at idle and when driving but it is not good for fuel economy and potentially for the engine and a set up that is too rich will cause more issues sooner.

 

Up to you what you do of course making assumptions is not the same as checking, you have altered the valves so the running will be different from before, you also need to check and adjust as required, or replace worn or faulty items as required, points, plugs, timing and mixture  again, in that order.

 

I cannot remember, was old petrol drained from the tank or fully used up by now and new fresh petrol in the tank?  If you are still on old fuel left in the tank from the car sitting around a long time do you know if any fuel stabiliser was added to the tank to allow for the period  of the car sitting unused?  Given you have a fuel problem I would empty out any previous fuel, easier done with an electric fuel pumps that mechanical, then fresh petrol in the tank with proportional amount of petrol system cleaner in.  With the fresh petrol fuel and petrol system cleaner if possible drive off about 5 litres of petrol  in one drive and then do all the ignition and mixture set up checks and possible adjustments.  If the car cannot be driven to use up the about 5 litres then the ignition and mixture set up checks and possible adjustments will have to be made before driving off the fresh fuel.

 

Cars that sit around and are not driven far enough each time and frequently enough get problems and issues from all the lack of use for the whole car not just the engine.  With an old car new to you you need to drive it to find its issues and problems to be able to sort them out.  Many/some of these issues can be prevented by a staggered, between driving the car, full and proper service, checks at least, of the whole car (not just engine) equivalent to a 60, 120,000 km service or 5, 10 years.  Your car is 28 years old when do you think it last had a 5, 10  year service, perhaps 23, 18  years perhaps never, when did it have a 1, 2, 3 year service.

 

Old cars that look good are not necessarily good runners or in good mechanical or electrical condition, your engine bay looks very good but the engine has a running problem, hopefully fairly easily sorted, there looks to be plenty of good potential.

 

Perhaps others members could chime in (post) with other, different, ideas, knowledge (training) and experience and ways of putting things.

 

Okay, so it came out that when the flap opens, it almost closes the warm air intake, so I removed it (the flap). I also blocked the cold air intake so the only air coming in could be warm. It got better, car started stalling at the similar time but throttle worked a lot longer. It seemed like the ice could melt a bit when at lower rpms and that kept it going at least 25 min. It sometimes cut out but started working again. The car did stall like 60% of the time when pressing the clutch in but that seemed enough for it to stay running just a few sec after that.

Edited 8 February, 20251 yr by RalfRannet

On 29/01/2025 at 00:28, RalfRannet said:

when turning in the CO screw (it should cut off fuel).

CO screw adjusts idle air. It is not related to fuel.

 

On 29/01/2025 at 00:39, RalfRannet said:

when its almost fully in the revs drop a bit and the car struggles to keep the revs. Really starts moving up and down (+-100).

You have air leak.

%90 percent sure.

 

In my carb, I don't have to fully set the screw in to see the revs dropping.

When the screw is fully in and the car is still running, this means it sucks air from elsewhere.

 

If the carb gaskets are OK, check brake booster hose. Disconnect the hose and plug its insert on the carb too see if there is any change. (Don't forget to reinstall it before driving)

Check all of the small hoses around the carburetor. (Second stage, TTV hoses) for cracks and leaks.

 

Some people spray lighter gas around the carb gasket to see if that is rising the rev. I find it dangerous. You can use an incense. By keeping it close to the gasket mating areas you might see the leak.

 

Your idle system's fuel routes might be clogged too.

 

Please, remove the air box and run the engine with the carb's top open.

Listen to the carb from close.

You must hear a constant hissssss from intake of the carb. Like listening to a vacuum cleaner's hose's end.

 

If you hear, hissss....gro...gro...glog.hissss.glo..glog...hisss... that means vacuum leak.

I think the leaks are fixed by now. Turning in the CO screw now kills the car and the revs drop as they should. The idle is smooth, no movement in the rev gauge. Hiss sound is constant and spraying carb cleaner doesn't increase the revs as it previously did. If you have any ideas on how to prevent the carb from icing, it would be very great. It does get only warm air now, the pipe going to the air filter was really warn, not hot (it doesn't burn my hand) and the air filter housing was also warm and it still froze. (-6°C  when testing).

13 minutes ago, RalfRannet said:

If you have any ideas on how to prevent the carb from icing, it would be very great. It does get only warm air now, the pipe going to the air filter was really warn, not hot (it doesn't burn my hand) and the air filter housing was also warm and it still froze. (-6°C  when testing).

Well, AIUI you're looking at the wrong figures. Carb icing is caused by high relative humidity inside the venturi (throttle body) leading to ice forming, making it narrower, and accelerating the formation of more ice there...

Yes I know, I think that temp. also plays a role (it just hasn't happened in warmer weather for me). Anyways how could one fix that then? I've heard that closing the choke plate could help (making the choke manual).

2 hours ago, RalfRannet said:

I think the leaks are fixed by now. Turning in the CO screw now kills the car and the revs drop as they should. The idle is smooth, no movement in the rev gauge. Hiss sound is constant and spraying carb cleaner doesn't increase the revs as it previously did. If you have any ideas on how to prevent the carb from icing, it would be very great. It does get only warm air now, the pipe going to the air filter was really warn, not hot (it doesn't burn my hand) and the air filter housing was also warm and it still froze. (-6°C  when testing).

After the engine start, could you check the thick hose going to the top of the radiator? After the engine start up, the thick coolant hose must stay cold until the thermostat opening.

If the thermostat is stuck open, maybe the engine can not heat up properly.

 

My hot air intake is completely disabled and sealed off. I don't even have the air routing plate on the exhaust manifold.

Even below -10ºC carb doesn't ice with LPG.

I've never experienced carb icing so far.

 

But, that doesn't mean the carb should get ice without LPG. It's built in Czech Republic after all.

If I were you, I'd reduce the fast idle from 1500rpm to 1000. Let the engine warm up without too much air velocity through the carb.

I use fast idle to compensate the cold state hard turning of the engine.

On 08/02/2025 at 17:42, RalfRannet said:

when the flap opens, it almost closes the warm air intake,

Which flap, chole flap or air intake temperature flap?

 

 

2 hours ago, RalfRannet said:

It does get only warm air now, the pipe going to the air filter was really warn, not hot (it doesn't burn my hand) and the air filter housing was also warm and it still froze. (-6°C  when testing).

That to me sounds warm for setting idle mixture, you want ted engine warmed up but things not too warm otherwise the mixture will be wrong for running along the road with air coming into carb and engine bay and engine bay exiting.

 

 

1 hour ago, RalfRannet said:

closing the choke plate could help (making the choke manual)

Fully opening the flap would be equivalent to choke off, no choke.  Manual choke was a system a fully mechanical system, on my cars at least increasing the idle speed same as pushing the accelerator pedal and then enrichening the fuel mixture, this was variable within limits (stops) by pulling a choke cable knob that would hold it's position and the driver would adjust as required, pushing the cable back to rest position when the choke was no longer required as the engine had warmed enough to no longer need choke (I hope that makes sense, I no longer have a Driver's Handbook that would fully describe and show the operation in drawings).

 

My guess has been and remains that the mixture may be too rich which if not causing the icing certainly will not help it but that is only going on the information given in this thread.  Which is why I think you should go through that ignition chain as described before and check/reset the carb settings as required.  Of course I could be wrong and this may not be the only issue causing this even if I was right.

 

9 minutes ago, R_Blue said:

After the engine start, could you check the thick hose going to the top of the radiator? After the engine start up, the thick coolant hose must stay cold until the thermostat opening.

If the thermostat is stuck open, maybe the engine can not heat up properly.

I changed the thermostat very recently actually because it was stuck open, when driving the engine temp went down to 0. Now it gets up to temp fine and mostly stays below the middle line.

9 minutes ago, R_Blue said:

My hot air intake is completely disabled and sealed off. I don't even have the air routing plate on the exhaust manifold.

Even below -10ºC carb doesn't ice with LPG.

I've never experienced carb icing so far.

But, that doesn't mean the carb should get ice without LPG. It's built in Czech Republic after all.

If I were you, I'd reduce the fast idle from 1500rpm to 1000. Let the engine warm up without too much air velocity through the carb.

I use fast idle to compensate the cold state hard turning of the engine.

How interesting! I'm not running on LPG, but does your carb happen to have the heating element on the back side of it? On this website it correlates to number 37, it sits just below the idle cut-off valve (8).

8 minutes ago, nta16 said:

Which flap, chole flap or air intake temperature flap?

Air intake temp flap that I now removed and blocked off the cold air pipe completely.

8 minutes ago, nta16 said:

That to me sounds warm for setting idle mixture, you want ted engine warmed up but things not too warm otherwise the mixture will be wrong for running along the road with air coming into carb and engine bay and engine bay exiting.

It doesn't get too warm inside the carb, never will. The mixture is set so that it idles smoothly and runs well.

8 minutes ago, nta16 said:

 

Fully opening the flap would be equivalent to choke off, no choke.  Manual choke was a system a fully mechanical system, on my cars at least increasing the idle speed same as pushing the accelerator pedal and then enrichening the fuel mixture, this was variable within limits (stops) by pulling a choke cable knob that would hold it's position and the driver would adjust as required, pushing the cable back to rest position when the choke was no longer required as the engine had warmed enough to no longer need choke (I hope that makes sense, I no longer have a Driver's Handbook that would fully describe and show the operation in drawings).

I understand. On the carb, the choke flap sits on top and when it's closed, it pulls more fuel through a different place, bc the idle cut-off valve doesn't kill the idle anymore. That in theory should allow the engine to stay running even if the main fuel "pipe" freezes. 

8 minutes ago, nta16 said:

My guess has been and remains that the mixture may be too rich which if not causing the icing certainly will not help it but that is only going on the information given in this thread.  Which is why I think you should go through that ignition chain as described before and check/reset the carb settings as required.  Of course I could be wrong and this may not be the only issue causing this even if I was right.

 

I may be wrong but it can't be too rich, bc when the screw is turned in more, the idle gets rough and the car dies. The CO measurements came back as 0.2... and the allowed was 3.5 so if anything it's running a bit lean.

13 minutes ago, RalfRannet said:

How interesting! I'm not running on LPG, but does your carb happen to have the heating element on the back side of it? On this website it correlates to number 37, it sits just below the idle cut-off valve (8).

No, there is not any heating element like that.

 

Something happened to me which might worth checking for you.

The gas pedal started to get stuck, at the  same time all of my carburetor fast idle and idle speed adjustments were gone.

I discovered that, the gas pedal wire had lots of friction.

I removed its end from the carb and lubricated it using a syringe filled with oil. I inserted the needle between wire and its sheath.

After patiently oiling, I saw rusty oil coming from other end of the gas pedal cable inside the cabin.

All of the problems disappeared after that.

 

I've bought a new cable but forgotten to install it.

A good call as sticking could be away from point of idle, not noticeable under foot and pedal and carb return to normal resting so not showing up at idle.

 

Also free movement of accelerator pedal, pivot point or bush if pendant type or hinge if floor mounted type.  If accelerator cable is bent or frayed it best replaced.

 

Again it might not be cause or sole cause but worth checking on an old car new to you if you have not already done so.

 

Sorry for the long silence, the car is really eating away at my patience and it doesn't seem to be a simple issue. The throttle cable doesn't get stuck. But a new problem has surfaced, possibly the same as suspected "freezing". For weeks now, the car hasn't idled. It just dies. It started happening after I added some fuel additive that should increase the fuel freezing temperature, but it shouldn't be a problem because I also have tried running the engine from a gas canister with good fuel. After adding different silicones, gaskets, etc, to the carb main gasket (between the manifold and carb), it still doesn't work. I even ordered a new flange and added reinzol silicon gasket, which now sometimes lets the car idle at 500 rpm. I still suspect that it's an air leak bc when spraying carb cleaner, the revs increase, also I can't see that much fuel being pulled into the barrel. Still happening after the choke flap has opened. But driving in warmer weather, the accelerator pedal stopped working again for a few seconds, then started, stopped and so on. I have cleaned the different holes again, but I can't figure out the cause. My theory is that it doesn't get enough fuel at times. But could a mechanical fuel pump fail like that or does the float get stuck at a similar time every time?

I thought you were going to try an electric pump to rule out the mechanical pump.

Have you taken the cable ends off to check free movement by hand keeping the cable in position and any bends check free movement of accelerator pedal connection and linkage (if it has any) and free movement at carb end and connection and linkage, if it has any. Visually inspected outer and inner cable for fraying or catches on outer casing.

Are you sure the carb is fitted fully correctly and set up fully correctly. - I once had an American carb (Holley) and it was pulling engine oil and what felt like shutting down one bank of cylinders at a certain range of revs. The car was with an "American carb expert" for a week and he couldn't find anything so I took it to an old school English car and carbs tuning chap and after 20 minutes of looking and trying stuff he pulled off one of the vacuum pipes and blocked it off with a large screwdriver and then the carb and engine ran well through the problem rev range. An unnecessary vacuum line had been used and blocking engine and carb ends solved the issue, no more of my expensive engine oil was burnt and the carb and engine ran as they should.

That's me out of thoughts, ideas and stories again.

13 hours ago, RalfRannet said:

I added some fuel additive that should increase the fuel freezing temperature,

Carburettor icing is not fuel freezing

On 09/02/2025 at 20:45, nta16 said:

My guess has been and remains that the mixture may be too rich which if not causing the icing certainly will not help it

The air/fuel ratio will play no part in the phenomenon.

Carb icing is freezing of water vapour when moisture laden humid air (warm air contains more moisture) cools to the dew point from the pressure drop in the venturi, fuel vaporisation from the main jet can also drop the temperature (latent heat of vaporisation) of the incoming air.

In either case or frequently both together its the formation of ice particles that block the flow of fuel from the main jet, idle jet and progression drillings.

I finally got a new fuel pump, but that didn’t fix the issue. So, I checked the fuel level sensor (which I had replaced) in the tank and noticed that the filter could block the pipe at times. After securing the filter with a clamp, the gas pedal worked consistently during testing.
Now, I just need to fix the leak in the base gasket, and it should run perfectly. I also don’t think carb icing was ever the problem.