4CV CARB PROBLEMS

[MIRABELLE]

I know this maybe off the usual type on here but here's hoping. I have recently aquired a 1956 4CV which has been well restored. It is fitted with a Solex 22 ICBT and has an automatic choke from the exhaust heat. This seems to work OK now I freed of the spindle that the spring turns. I have had the carb appart and cleaned it. I have fitted a new little rubber diaphragm. Although I don’t know what this does.The problem I have is I cant get it to idle smoothly after it gets to working temp. The volume control screw ((W) on drawing) has no effect. The spec says screw home then out 3 turns. But this screw does nothing at whatever setting. It does not hunt so not rich it seems to be running weak. I suspect it may be a problem with the auto choke but not sure. I am at a loss where to look next, so any ideas please.

 

[André4Renaults]

It's possible there could be an air leak from some of the gaskets in or around the carburettor. From experience it's likely to be the gasket between the carburettor and the inlet manifold. Try tightening the securing nuts and bolts & see if this helps. If the gasket look damaged or worn, perhaps hunt down a new one.

Another problem may be the in float chamber. If the float doesn't "float" in the petrol then the pump will push far too much petrol through the carburettor, which would make the engine run too richly.

If the volume screw is having no effect it might be damaged.

These are. a few ideas. If you were in the U.K. I would recommend a good carburettor repair company to you.

 

[MIRABELLE]

Thanks for reply. I had tried all the usual things like leaks, gaskets. So today had a brainwave and thought it could be the volume screw, (as you mention above) so took it appart and found the tip of the screw was broken off and jammed in the body. Managed to get it out OK now got to make a new screw. A couple of pictures attached ( if I can find how )

 

[MIRABELLE]

Another question. I replaced this litlle rubber diaphragm with a new one as the old one had gone hard, however I have no idea what its function is. Any iea?

 

[Homegrown]

Another question. I replaced this litlle rubber diaphragm with a new one as the old one had gone hard, however I have no idea what its function is. Any iea?
View attachment 33205

Have no specific knowledge about your carb but usually it’s a diaphragm for the acc pump (pushes in extra fuel when you push down accelerator quickly) for better throttle response

 

[André4Renaults]

I'm glad you've found the cause of the problem! I should think new mixture screws can be obtained.

If the diaphragm is damaged air will leak past it and the car won't accelerate quickly. As explained above the accelerator pump pushes a "shot" of petrol into the carburettor when the pedal's pushed hard down (overtaking, for example) so if it's damaged the car will accelerate, but only slowly. It will "pick up speed" but not "nip" if that makes sense!

While you have the carburettor off the car why not buy a kit of gaskets and change them? It'd be a pity you have to go through the removal process again at a later stage to replace the washers & gaskets within it.

 

[MIRABELLE]

Thanks for the responses. I obtained an overhaul kit which is where the diaphragm came from and it included a set of gaskets and a new shut off valve for the float. I have a lathe so it will be a lot quicker to make a new screw than try and locate one,

 

[angel]

This is not an accelerator pump, it is a weakening or enrichening device (depending on carburettor) operated by vacuum inside the carburettor. It will affect idling if punctured or stiff, so even if it has been replaced, check that the faces of both the carburettor and its cover are perfectly flat.
Check also that the carburettor base is not warped, very common on Solex carbs that are located over an exhaust manifold.

 

[Piet]

I would seriously consider putting a larger carb from a dauphine or R4 on it. Trying to tune tiny tiny carbs, especially seventy year old ones, just does my head in.