Hi
Noticed something abit awry with the running on my 2CV a 1977 2CV6 with single choke carb.

At 60mph cruise the car seems to pulse and surge almost like a misfire or like its suffering from fuel issue.

So far the following items have been replaced

Carb (new one fitted)
Coil
Plugs (B7HS)
HT Leads
Ignition system (123 now fitted)

Fuel pump seems to be OK, so can anyone suggest any other things I should look at to cure this issue.

Matt,
sounds like a weak mixture, don't forget that a single choke carburettor will run lean
on unleaded fuel, just like its twin choke counterpart is known to do.

I'd suggest that you try a main jet 2 steps larger than what's fitted at present, so if
it's got a 155, you should move to a 160. ( Jet sizes increase in steps of 2.5. )

ken

Hi Ken

The replacement Carb I got was a Solex 34 PICS - 10. The only listing I found for this carb was in the Autobooks Manual for 2CV / Ami and it shows its for a 3CV Van.

When I took the cover off before fitting I noticed that the jet sizes were different to the original 34 PICS 6 carb I took off and I think the Pimary was larger as was the Air correction Jet. I don't have details to hand right now but if you have the Autobooks manual can you double check the jet sizes for a PICS 10. I didn't swap over any jets and I'm running it out of the box.

If the main jet is larger and the air correction jet is also larger should I use the smaller air correction jet from my PICS 6 to richen the mixture?

I did at first think it was a sticking needle jet as it feels like that symptom but not as drastic. Needle jet was fine though.

The C42S plugs I removed prior to fitting the B7HS ones were clean, perhaps too clean with not a univeral coating of grey/brown.

Matt,
34 PICS 6 would have had a 155 primary jet and an AB corrector jet, 34 PICS 10 equivalents being 165 and AC.

If an AB air corrector jet has a smaller bore than an AC, its effect will be to richen the mixture at higher rpm & mixture flow, so worth a try.

ken

I will give it a go. I've noticed that this carb is much better than the PICS 6 in that it goes well, and makes the car more torquey somehow could this be due to the fatter main jet?

Matt,
it's not always the case, as too rich a mixture will also result in less power, as well as damaging your bank balance.
Anyway, the rule is to change only one thing at a time, so it will be interesting to hear what the effect is of swapping the air corrector jet.

Ken

Just an update

Fitted the AB air corrector jet to my 34 PICS 10 at the weekend and noticed a marked improvement in running at 60 mph, so this is possibly the cure.

However also noticed that the preheat pipe is holed so managed to bodge a repair with a beer can and a jubilee clip, whilst I collect the bits together for a manifold swap, blimey it keeps me busy this car.

ah! the balance pipe has a marked effect on the way the engine runs

mine has a bit coke can and sme tying wire ....one day!

I was forced to drink a can of beer so that I could repair the hole. I used a Mackeson's Stout can (it was all I had) and by some quirk of fate my manifold appears to read "Alcohol 3% Per Volume".

Funny that but its kind of true if they are slinging ethanol in the unleaded now

Also my spare manifold appears to be different to the original having a bigger hot box under the carb which extends forward.