Thanks I'll take another look

Have you checked the valve clearances?
I had a similar problem,fluffing and farting on change over from first to second throttle opening,and bad starting when hot.It was suggested to check clearances to resolve the starting problem which it did,but it also sorted the fluffing problem too.

Bugster,
if the accelerator pump jet is loose enough to fall out, that usually means that the O ring which should hold it in place has failed.
Fuel then leaks out at the joint between the carburettor lid and body, rather than being delivered into the carburettor throat via the nozzle.
Also, how long is the duration of the jet of fuel if the operating lever is moved by hand?
It should be about 3 to 5 seconds...

As Gaz has already advised, those choke pull-off devices are a very common source of air leaks, so it should be checked and disabled if it's faulty.
There's not much point in having a useless ornament fixed onto the top of the carburettor, even less if all that it is doing is acting as a conduit for air to leak into the manifold.


Limiting travel of choke flap. by slcchassis, on Flickr


How big is that split in the intake hose? Is it large enough to allow the hose to collapse inwards when the throttle is snapped open?

Will that do for now?

ken.

Thanks dave, ken and gaz, That's plenty to investigate hopefully this weekend. Will definitely post the result.

Well I finally allocated a day to this problem and followed the suggestions.



I couldn't find an O ring that was identical so fitted 3 smaller ones which gave a nice push fit and tested it for leaks - ok. Duration of jet of fuel is about 3 seconds.



I made a blanking gasket and fitted this under the pull-off device with a smear of sealant.



I applied further sealant to the air intake hose and no signs of it collapsing when the throttle is floored. The splits were tiny, about 6mm.[/quote]



Err thanks ken but still struggling I'm afraid

I had the carb apart again (should have fitted wing nuts by now ) and triple checked everything was clear again. Reassembled it, applied thin coat of sealant to the manifold gaskets and refitted it (paying particular attention that the small jet on the underside wasn't blocked).

Reset valve clearances, exhausts were down to .003" and .004", and inlets .007" and .006". Checked compressions (cold I'm afraid, I know hot is better) with plugs out and full throttle, n/s 155 and o/s 145psi. Squirt of WD40 in cylinders gave 160 and 165 respectively.

Turned over engine on starter and there's a good flow of fuel from the pump.

Refitted NGK B6 plugs (done about 250 miles from new). started engine and let it warm up for 10 mins. Readjusted idle emission control slightly. Booted throttle and the engine completely died. Tried this several times with the same result. Actually worse than before when it would hesitate first and then pick up.

Wondering what to try next I spotted some old spark plugs from my Beetle (I think - I never throw anything away), probably done 2000 miles, Bosch W8AC, so as the thread length was identical and both cars are air cooled I thought what the hell and fitted them. This time flooring the throttle gave an instant response with no sign of hesitation, and the engine ticked over more smoothly.

So went for a road test and the performance is much as before - hesitation at constant speed, e.g. 30mph in 3rd, and acceleration is like a collection of flat spots as though it is starved of fuel. On a long flat straight I managed to reach 62mph.

So now I'm wondering whether it might be the much mentioned hose at the tank having an air leak?

So thanks for the advice so far and any more warmly welcomed

Had same problem with a 2cv6 (double bore) last week. Stripped the carby completely only to find it stuffed with shit and badly corroded. Tried to clean and re-jet the carby, using a carby kit but to no avail.
Fitted a re-conditioned carby from professional Dutch company. Huge improvement but still hesitation on the last 20% of the throttle. After speaking with the company over the phone, re-jetted to 90/120 no improvement at all. Fitted one more carby and voila all problems gone. All carbys 26/35.

Isn't the compression a bit low?
Dropping the tank takes all of 10 mins
Fitting it makes you throw tools, swear, and want to burn the car
Patience is needed

Bugster,
seems to me that you've got 2 separate faults, one with the accelerator pump or its jet, and the other is beginning to sound as though there's a problem with delivery of fuel to the carburettor.

If you work the accelerator pump lever by hand, does it move back into contact with its operating cam straightaway? Movement of the lever can become sluggish if the car has stood for some months, so it's common on 'Summer use only' cars.
Spraying WD40 or similar onto the mechanism and working it by hand usually frees things off...

For the other problem, try tackling a hill which has a layby near the top. Go at it with full throttle until you can pull into the layby and switch the engine off immediately.
Remove the carburettor lid and check the level of fuel in the bowl(s) and if it's too low, that would confirm where the problem lies.

Before you try that, I'd suggest getting rid of those VW plugs, since they're too hot a plug for use in a 2CV engine, equivalent to B5HS.

ken.

and while doin these carb shenanigans rather than trying wing nuts you can use just 3 of the carb lid screws , front middle and 2 back corner ones

Thanks everyone for the advice.

ken, the accelerator pump works ok always returning quickly. The actual spray continues for about 3 seconds operated manually. I have stripped and cleaned the carb 3 times now and it has a new accelerator pump diaphragm.

Unfortunately we have no suitable hills with lay byes at the top within 10 miles of here so I re-read James's post and thought why not drop the tank? I also read an old thread of ken's recommending disconnecting the fuel line at the front and removing it from its clips along the chassis to give more length in the petrol tank area when refitting. Great advice thanks - makes the job so much easier. I thoroughly checked the sender unit and the earth while the tank was out - reading from 2.5 ohms full to 325 ohms empty. And checked for continuity after the earth cable was fitted.







I also cleaned the electrical connections on the sender, blew down the sender fuel pipe under water to check for pinholes and immersed the float in warm water to check for bubbles - all ok. The sender is in excellent condition, the filter clear as a whistle, and the tank itself was spotless inside after a couple of vigorous flushes.

The piece of hose from the tank pipe to the nylon fuel line had no hose clips, just pushed on, and it's marked with chevrons and the name Rennes. Could it be the original factory fitted one? With no hose clips?



All back together now so I'll test it tomorrow hopefully.

Oh and I learnt another thing about the car, when the gauge is on empty there's about one gallon left

Cheers

Keith