Bubbly fuel causing cut off and fluctuating idle

Hello,

Recently I was struggling with constant cut offs and idle problems on my 1.3 driver with Solex 34 pic(t) 6 carb (the vapour trap version) and GF engine.
I was going mad, I almost replaced everything I could think of, fuel filter, fuel pump, flange, carb rebuilt, fuel hoses, air filter, but nothing worked.
I checked the vapour trap but it was clean an the fuel flows in it as it should be, the fuel pipes between the tank and engine bay were also clean.
And at this point I was out of ideas, but than a friend was telling me that he never saw so unusually bubbly fuel before, at that time I ignored it.
Than I was out on a test drive and the car got weak uphill and a few seconds later the engine was off so I was trying to do something to get it running again and I changed the hoses between the pump's intake and the vapour trap's return because the fuel filter looked a little dirty.
So without a fuel filter on the intake the car started almost instantly and after that it didn't stoped again than I bought a new fuel filter installed it and a few minutes after that the engine cut off again, I popped the hood started the car and I noticed the bubbles what was pointed out earlier by a friend, and actually the bubbles increased when I pressed the throttle to a point where the fuel wasn't enough. So I removed the filter, started the car and I noticed there are no bubbles in the fuel line and since than the car is running fine, no cut offs or iddle problems or loss of power but now I'm affraid that the vapour trap, and after that the carb will fill up with junk without a filter.

Is there any way to prevent the fuel from bubbling if the filter is installed, or is there a better filter for the 1.3 engine than this: LINK ?

Those little inline filters are normally what's fitted to those models, normally they're not a problem.

I would start by looking at how tightly the pipe fits the filter, if it's not that tight then you could be pinching the pipe when you do the clip up, and opening up a tiny gap for air to get in. It needs to be an almost exact fit for a fuel and air tight seal.  

Mike.

Thanks for the reply.
Now I replaced my clear hoses before the fuel pump to a double layer normal black rubber hose and I also put on clamps but what I don't really understand that why is it so loose on the fuel pump and is so tight on filter.
on the pump I had to tighten the clamp really hard and I can still rotate the hose but when I had the clear hose on, it fitted perfectly right away without clamp.
Here is a video of the bubbles with the refitted fuel filter, it's a little hard to see because I recorded it with my phone. In the video the bubbles are in an acceptable amount it was much worse before but I think it's still to much.
And when I put the filter back my idle droped at least 50rpm, so I had to adjust it.

You shouldn't get any bubbles in the fuel, there is air getting into your fuel line somewhere.

I'm struggling to see where that hose you were filming lines up in your fuel system, normally you have the line from the fuel tank into the in-line filter, then from the filter to the inlet on the pump, then from the pump to the carb - which section of hose was this?

It was the line which goes to the carb or in this case to the vapor trap, I didn't film the inlet because I replaced the hose to a black rubber one.
The only place I can think of is still the filter where the air can enter the system but I don't know how. This double layer hose fits so tight on the filter that there is no way there is a leak. And at the incoming metal pipe I pushed the hose down about 10cm-s and there is also a clamp to keep it in place.
The other point I can think of for air leak is the pump's intake because as I said the hose is a little loose there even after tightend really hard.
The fitting on the pump where you can put the hose on is really short, just a few mm longer than a clamp.

Piszi said

The fitting on the pump where you can put the hose on is really short, just a few mm longer than a clamp.

That doesn't sound right, normally they're a good few CM long with a little 'bubble' that you have to push the hose over like this picture.



Look at it carefully, you sure it's not snapped or been cut short? Sounds to me that is your most likely culprit.

Mike

No it's not and I wrote in my first post it's brand new but if you don't count the conical end of the fitting than it's about 3mm longer than the clamp which is good for the 6mm hose.
this is the pump I have I think it's brand is Unitehna:

Piszi said

No it's not and I wrote in my first post it's brand new but if you don't count the conical end of the fitting than it's about 3mm longer than the clamp which is good for the 6mm hose.
this is the pump I have I think it's brand is Unitehna:

Just because something is brand new does not always mean it's going to work 100% or has been manufactured correctly, trust me on that. You made it sound like the whole fitting was too short, I was only trying to help you.

A suggestion would be to draw fuel from a container other than your fuel tank, i.e take a fuel line from the filter and get it to draw fuel from another source, a half full petrol can will suffice, see if you still get bubbles in the fuel, but please be careful if you try this for very obvious reasons.

Mike.

Ok I know that a brand new part can be faulty I just wanted to say that the fittings aren't cut off or broken.
I did make a new video comparing 3 scenarios with new(ish) clear hoses, one without the filter, one with filter and one with the filter after the pump. link to video
There are bubbles in all 3 ways but the most are if the filter is before the pump. You will see that there are few bubbles coming out from the tank  but it gets much worse when the fuel comes out of the pump.
I read somewhere on another forum that wrong timing can cause bubbles in the fuel I can't check that because I don't have a strobe but it is possible that the timing is off.
Or I don't know if is it possible to bleed the fuel pump like a water pump because lots of water pumps can't bleed themselves and the air is stuck inside.

I did not tried yet what you suggested but thats the next on my list

So, today I replaced the two hose at the fuel tank (I think those were the original factory ones ) and the bubbles stoped coming from the tank and the car runs fine with the filter in, but I did noticed that after every few turn on the pump's out some bubbles appearing than for few turn nothing and than again.
Could this be because of wrong timing?

I dont see how timing could have anything to do with bubbles in the fuel as bubbles surely appear when air is getting into the fuel lines, are the bubbles now only after the fuel pump? because I bought a new fuel pump thinking my old one was not giving a good enough output and found that the new one which was the exact same make and everything was pants, it hardly pumped any fuel and was sent straight back so I wouldn't discount this being your issue!

I don't know how as I wrote I read that somewhere else, and I thought I should ask.
Yes the bubbles only appear after the pump. From the tank to the filter and after the filter the fuel is clear, no bubbles.
Maybe I should put my old pump back and see what happens. But I think I lost the rubber O-ring(gasket) which should go between the pump and the engine.
Does anyone know the dimensions of that (diameter and thickness)?

Yeah its worth trying you old one, what was wrong with it?

Actually I think nothing I was just trying everything to get the car running normaly and back than when I replaced it I had normal black rubber hoses and I didn't saw the bubbles so I assumed that the pump is wrong and pumping enogh fuel.

So, yesterday I put my old pump back and it works as it should be and it doesn't have bubbles on the outgoing flow so I think the new pump has a bad gasket.

But sadly I still have this bubbling problem which only starts after a few minutes when the engine strats building up heat.
Right now the only thing I did not replace is the metal fuel pipe under the car. But I don't think it has a leak because I don't see any fuel drops under the car or in the engine bay. And I put on double clamps on the hoses just to be sure, and because at the tank out (on the fuel level sender unit) the hose fitted a little loose.

Now I don't know what the hell causing this.
Is it possible that the return flow pushes to much air in the tank and that makes the fuel bubble?
Or can the fuel system pick up heat in the back of the car which could make the fittings loose?
Or can the vacuum get weaker when the enginge heats up?
Or what else could be?

I might swap one of my hoses and see if I have any bubbles because I cannot think that air is getting in because if air can get in then fuel could get out! which you would notice!

The fuel won't necessarily get out if air gets in because the mechanical pump is sucking the fuel from the tank and it is not under pressure like in modern cars where the electric pump primes on ingniton to pressurize the fuel system. And when you stop the car the most of the fuel will flow back to the lowest point and if a leak is at a high point you won't see fuel coming out.
But what do you mean by swapping the hoses? I just bought brand new 6mm Semperit hoses and replaced all even the little one inside the tank.

I mean, I will put in a clear hose in my system and see if the same thing is happening to my car

Actually I'm looking for a shop where I can buy new metal pipe but so far no luck and brass pipes are not allowed by the authorities here in Hungary. And the rubber hoses as I wrote before are new so they are clean (at least were unti I installed them )

Ok, I might fund the problem. There was a rock an a piece of rusted metal in the pick up line of the fuel level sender unit and it was stuck hard because compressed air did not clean it out it only got out after I pulled a shoelace through it
Than I baypassed the original fuel line with a long clear hose to see whats happening and fuel is bubble free but I'm pretty sure that I have to clean the pipe under car before using it again.

And now I have a new problem which wasn't present until now. After the engine reaches operating heat on acceleration the car loosing power for a sec and back to normal and looses again and back again and so on. The idle is ok the car iddling at about 900rpm even with the lights on.

Maybe the carb or the vapor trap is full of dirt because I used the car without fuel filter or maybe I under calibrated my DIY filter (a brass pipe with ten 2mm holes on it and the end sealed) in the tank but than the problem should be present even with cold engine and chookie on.