Classic cars forum & vehicle restoration.

[Rick]

Spent some time on the 4CV this evening, I installed a throwaway fuel filter in the line up to the carb (I'd usually put one before the pump but I have a theory that any muck is coming from the pump, rather than the tank). After a few miles it's already showing evidence of dirt in it so I might be swapping this filter a few times. None of the fuel pipes had clips on them so I rectified that while I was at it.

I also checked the plug gaps (all too small), the plugs had been put into the aluminium head very tightly by a previous owner, something I didn't repeat when I put them back in, with a dab of copper grease in each instance.

The points gap was also very tight and was, happily, a doddle to re-adjust, I look forward to taking it out for another run asap to see if there's any difference.

RJ
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[alastairq]

Is the fuel pump mechanical?

Perhaps the diaphragm is starting to break up?

I would be inclined to plumb in a modern electric pump [cheaper anyway these days....modern Facet pumps are plastic..although their mounting procedures are somewhat different to the metal Facet types] into the fuel supply, close to the tank. Maybe wired up through a switch from the 'ignition' circuit?

I believe they can be inactive, with the mechanical pump pulling fuel through them...but for priming purposes, and taking over if the mechanical pump gives up [as has happened?]....a flick of a switch can bring instant recovery.

In the US of A, where high alcohol content of fuel has been a fact of life for quite some time now, there have been solutions to the issues of hot starting, priming, flashing off due to engine heat, etc....due to modern fuels being made differently....These solutions have often involved the use of electric pumps,and also, small bore fuel return set-ups, to allow fuel to be constantly flowing round the circuit.

I firmly believe that we have to consider embracing these subtle changes in 'technology' in order to keep our oldies running as they should, in a very different [modern] automotive world.

Electric pumps don't have to be as complex, or big, as those provided by SU in past times, either.
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Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
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Ford Pop chassis, Ashley 1172 bodyshell, in pieces.

[Rick]

Spent a little more time investigating matters 4CV.

I may have mentioned already that someone replaced the standard Solex carb with a Weber. As a result I think this has contributed to the two problems I've had of late, ie being more sluggish that I think it should be, and occasional fuel vaporisation.

On the latter, studying photos of standard installations I noted that the fuel line should run to the forward end of the engine, passing close to the mechanical engine fan that blows backwards over the engine (the rad is mounted between the engine and the rear seat back effectively. This presumably to help keep it cool. The Weber's inlet is in a different position compared to the original Solex, but I've re-routed the line to more closely match the original and hopefully benefit from the close-ish proximity of the cooling fan. Previously it had been routed over the forward end of the engine, right over the manifold and well away from the main blast of the fan.

I also plan to make up a heat shield to protect the carb and line from the nearby cast iron exhaust manifold. This is a mod I've seen done on quite a few 4CVs.

Re the sluggish part, the linkage to the replacement carb has been cobbled up a bit and as a result operates at quite an angle whereas the original operated directly vertical from the pivot. I suspected that it wasn't fully operating the butterfly as it should. With junior operating the throttle pedal it became clear that the linkage was only opening the butterfly by about 20-25% or so at its maximum. If I disconnect the linkage there is a huge amount of extra movement available on the carb that isn't being used. I've ordered a generic fuel linkage and will try to improve the situation. I could perhaps try and find an original Solex 22 carb but most are in France, seem pricey, and would inevitably need an overhaul, so if I can improve the current setup then I will.

RJ
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