I have a '79 CX 2400 C-matic w/ carburettor. A friend of mine has the same car - but w/ 4-speed manual and A/C. (The funny thing is that both cars are green metallic AC 538 "Vert Dryades"- "fairy green" - a quite rare colour only offered for the model year 1979). Both cars was sold new in France and we aquired then in the Netherlands about 2 years ago.
I've found out that we both have the wrong carburettors! CX 2400 Models with A/C or C-matic (or both) should from model year 1977 be equipped with a Weber 34 DMTR 35/350 carb. (34 DMTR 25/100 or 150 for CX 2000 and 34 DMTR 28/100 or 300 for CX 2200 with options as mentioned).
It turned out that my CX was fitted with a 34 DMTR 35/250. The latter is for the basic CX 2400 w/o A/C or C-matic in '77 and early '78; from mid-'78 Citroën used a Solex 34 CICF 161 which what was we found on my friends car. The difference between these two carbs and what should have been there is that the std. carb lacks the "fast-idle" circuit.
The "fast-idle" circuit consists of a vacuum-operated device on the carb and an electrical operated vacuum valve mounted close to the right front wheel sphere. It opens or closes so that vacuum from the engines inlet via a rubber hose can or cannot be applied to the membrane in the "fast-idle device". I've managed to get hold of such an carburettor now, see attached photo w/ captions.The other photo shows how the tubes and vacuum electro-vale is connected. (Photo supplied by courtesy of Manabu Kosuge in Japan and is taken from his 1980 CX 2400 Pallas C-matic LHD).
The philosophy is that when you put the C-matic gearbox in gear the drag of the torque converter will lower the engine's r.p.m., and the "fast-idle" circuit will counteract that by feeding the engine with a little more air/fuel mix. The same applies to the A/C models, switching on the A/C activates the relay that controls the vacuum valve that in turn counteracts the drop in idle r.p.m.
I can confirm that it's hard to manoever the CX while parking in a garage-house w/o any "fast idle"-device, the idle is very low when "creeping" and the engine will easily stall. Compensating for low r.p.m. by giving more throttle is difficult as your right foot will be on the brake pedal and sudden "leaps" caused by attempts to keep the engine from stalling is not desirable...
The Citroën p/n for the vacuum valve is 5-426-080 and is made by Pierburg. This part seems to be a "dark horse" - it is "unobtainium" at all the usual CX parts sources (not even mentioned) and I have so far found no mention of it in this forum too. I know Aussie models may have somewhat different specs (RHD and 2nd rear mounted A/C) but I reckon that Aussie carb-models w/ C-matic and/or A/C also must have a fast-idle circuit.
(And there seems to be a lot of CX's in Australia both with C-matic and w/ A/C. In Europe it seems that if there was perceived any trouble whatsoever with a C-matic box the "cure" was to replace it with a manual, typically a 5-speed. And A/C was a luxury option and not a bare necessity as in Australia. So there are very few CX S1 around w/ A/C and/or C-matic here, at least carburettor models).
Anyway - I take my chances and ask you guys "down under" if anybody has any tips on where to find the "Vacuum electro-valve" p/n 5-426-080? And also the little drum-shaped white air-box next to it - p/n 5-491-311. Or suitable replacement parts for these. Thank you for any feedback!
I've found out that we both have the wrong carburettors! CX 2400 Models with A/C or C-matic (or both) should from model year 1977 be equipped with a Weber 34 DMTR 35/350 carb. (34 DMTR 25/100 or 150 for CX 2000 and 34 DMTR 28/100 or 300 for CX 2200 with options as mentioned).
It turned out that my CX was fitted with a 34 DMTR 35/250. The latter is for the basic CX 2400 w/o A/C or C-matic in '77 and early '78; from mid-'78 Citroën used a Solex 34 CICF 161 which what was we found on my friends car. The difference between these two carbs and what should have been there is that the std. carb lacks the "fast-idle" circuit.
The "fast-idle" circuit consists of a vacuum-operated device on the carb and an electrical operated vacuum valve mounted close to the right front wheel sphere. It opens or closes so that vacuum from the engines inlet via a rubber hose can or cannot be applied to the membrane in the "fast-idle device". I've managed to get hold of such an carburettor now, see attached photo w/ captions.The other photo shows how the tubes and vacuum electro-vale is connected. (Photo supplied by courtesy of Manabu Kosuge in Japan and is taken from his 1980 CX 2400 Pallas C-matic LHD).
The philosophy is that when you put the C-matic gearbox in gear the drag of the torque converter will lower the engine's r.p.m., and the "fast-idle" circuit will counteract that by feeding the engine with a little more air/fuel mix. The same applies to the A/C models, switching on the A/C activates the relay that controls the vacuum valve that in turn counteracts the drop in idle r.p.m.
I can confirm that it's hard to manoever the CX while parking in a garage-house w/o any "fast idle"-device, the idle is very low when "creeping" and the engine will easily stall. Compensating for low r.p.m. by giving more throttle is difficult as your right foot will be on the brake pedal and sudden "leaps" caused by attempts to keep the engine from stalling is not desirable...
The Citroën p/n for the vacuum valve is 5-426-080 and is made by Pierburg. This part seems to be a "dark horse" - it is "unobtainium" at all the usual CX parts sources (not even mentioned) and I have so far found no mention of it in this forum too. I know Aussie models may have somewhat different specs (RHD and 2nd rear mounted A/C) but I reckon that Aussie carb-models w/ C-matic and/or A/C also must have a fast-idle circuit.
(And there seems to be a lot of CX's in Australia both with C-matic and w/ A/C. In Europe it seems that if there was perceived any trouble whatsoever with a C-matic box the "cure" was to replace it with a manual, typically a 5-speed. And A/C was a luxury option and not a bare necessity as in Australia. So there are very few CX S1 around w/ A/C and/or C-matic here, at least carburettor models).
Anyway - I take my chances and ask you guys "down under" if anybody has any tips on where to find the "Vacuum electro-valve" p/n 5-426-080? And also the little drum-shaped white air-box next to it - p/n 5-491-311. Or suitable replacement parts for these. Thank you for any feedback!
The problem with buying aftermarket parts that contain rubber ... is they almost all seem to be complete garbage 