Hi

I still have a problem on my car (presented here viewtopic.php?f=5&t=5281 ).

The idle is really higher than what it should have been.

my engine A79/1 435cm3 is equiped with a solex 34 pics 6 carburetor.

It's the model with 3 adjust screw :
- throttle stop screw (is it the correct term in english ?) wich adjust the angle of the throttle
- pilot air/fuel screw located on the bottom of the carburetor
- "air screw" located on the top of the carburetor and used to adjust the idle rpm

The first two are on all versions of 2cv's carburetor, the third is less usual.

my problem is that : even if i unscrew the throttle stop screw until it doesn't touch the throttle and i completely screw the "air screw" to reduce at maximum the idle, the engine speed still to be too high !

I have checked if i have air intake on the intake manifold and i have corrected all ... I have tried various adjustement of ignition advance but i didn't manage to have a correct idle.

In have no idea to solve my issue and it's really unpleasant ...

Thanks a lot to all

Bye

Romain

Romain,
have you checked how much play/movement there is between the carburettor spindle (broche) and the body?
If that's badly worn, the air leak will make it impossible to obtain a low tickover speed; it's often cheaper and easier to find another carburettor which is less worn than to repair the one you have...

Almost forgot, in order to check, use a small syringe to drip petrol onto each end of the spindle, so you can gauge how much this affects the tickover.
If it's very badly worn, you will be able to detect the movement by hand.

Hi Ken,

Thanks for your reply !

Regarding the clearance between the spindle and the body, it not seems to be excessive but I had an air leakage. I detected this leaking putting a brush with petrol on the spindle, then the iddle lower.

When I disassembled, I've found that the outside diameter of the seal is not well fitted, there is a clearance between the seal and the body. I tried to stuck seals on the body and the leakage seemed to disappear.

I will try again with a syringe to be really sure

I also tried to adjust in the best way the throttle valve in the body in order to have a good sealing when the throttle valve is closed (iddle position) ... No positive effect ...

I'm sure you will take me for a fool but I have the impression that the iddle change when I am braking ... Be sure that I've not installed a brake assist ... Do you think the brake action force the engine to move (the position change) and it modifies the force applied to the spingle ? Is it only for this reason that the iddle move when I break ?

The whole carburetor has been clean in an ultrasonic bath and all seals are new ... I really don't undestand

Changes during braking could be soft or broken gearbox mount especially if you have a rod throttle linkage

Thank you Sean,

What do you mean by "soft or broken gearbox mount" ? I precise that i hear these changes when i am stationed, in neutral position....

Squirting WD40 or startpilot in the direction of the spindles will do the same trick..

Check also if you butterly/ies are really shut maybee theres corrosion there.. keeping a little gap all the time...
Take a good look if the butterfly/ies are really in the middle of the shaft, otherwise it will Always be open at 1 side.

Romain (& Sean),
even with the gearbox and engine mounts in good condition, the engine/gearbox unit will move a slight amount under heavy braking, as it absorbs the braking torque.
That's the whole point of rubber mounts, after all...

With a rod linkage carburettor, that small movement will tend to pull the throttle towards the closed position, so it might be worth increasing the tension of the throttle closing spring, which clips onto the rod.?

Thank you all.

Ipgo : i'll check a new time this weekend if there is an air leakage on the spindle.the shut of the butterfly is ok, i already have dismounted the carburetor just to check this point and i have tried to put the butterfly in the middle of the shaft to assure a good sealing when the butterfly is shut.

I didn't found corrosion inside the body i don't find a photo of the inside but i let you have a look to photos below ... inside is like the outside appearance ... Very great for me

Ken : you manage to explain in good english what i try to say regarding the movement of the engine during braking, thanks.

For all : do you think a defect in the exhaust manifold can produce this phenomenon ? If exhaust gazs come inside the inlet line ? I know that is an usual defect due tu corrosion but i don't now if it can be the origin of my issue ?

Bye

Romain

Hi all,

I haven't checked the air leakage yet but I will do ASAP.

However I had a look to a spare exhaust/inlet manifold I have and it's really worn... Exhaust tube is gnawed by the rust with big holes ... I wanted to try with another manifold but it will be difficult

Hi,

Please can someone describe to me the way to set correctly my carburetor ?

I Know the process for a classic carb with pilot screw and throttle stop screw but I try to use the same method on my carburetor with 3 screws and I'm not sure to be right ... I didn't find clear process on the web ...

Thanks in advance

Romain