223 Carb Issue

[2HP]

Dear All,

Hoping for a steer on how to approach a carb issue.

Background: 223 has been unused for 13 or 14 years, although I did refurb both heads 8 or 9 years ago to address poor head pressure (thanks to forum advice and spare parts from Calum!) - At the time I replaced damaged valves and also reringed the pistons using stepper rings - I had broken a ring when cleaning one of the pistons. The engine was tested running fine after I rebuilt it and cylinder pressures etc were all restored to spec, although I'm pretty sure I haven't had it out on the road for 13 or 14 years.

Standard dyane high compression engine with standard solex twin choke 24/21 carb, though there is evidence of the jets having been at least serviced (screwdriver marks).

Dusted the car off at the weekend and spent hours trying to start it. Removed plugs and sparking witnessed by earthing plugs and turning it over. Noticed that fuel had a wiff of what I would describe as 'petrol mixed with a little white spirit' so I guess it'd gone off and perhaps lost some of its volatility. Flushed out the fuel line and with fresh fuel & still wouldn't start, even after filling the pipe from the fuel pump to the carb with fresh fuel. Noticed fuel leaking from under the carb where the gasket is supposed to sit. Removed carb to find standard 2cv gasket had been removed and replaced with just a skim of now-disintegrated red something, possibly gasket silicon - In part explaining why fuel was leaking between the carb and the inlet manifold.

Squirted a teaspoon of fuel directly into the pots and into the manifold, all without the carb in place, and managed a few bangs, so that also confirms the sparks are probably OK.

Does the evidence of fuel pouring out under the carb, aside from the obvious gasket issue, indicate a float/needle crud issue?

I'm guessing the standard gasket had been removed by the car's builder to deliver more heat to the carb - The balance pipe has been sawn off and I recall that the car did sometimes suffer from fuel starvation (carb icing) when driving at speed in cold weather. So, should I just redo the carb to manifold seal with HT silicone? Or could I get away with 0.5mm HT paper/fibre gasket instead? Do I need to open the carb and check the float heights and needle seating?

Any pointers gratefully received.

[Jack602]

I sorted a similar problem yesterday on my Pembleton, which may or may not be related.
Background
I built my car last year using a 2cv donor that had been sitting in someones front garden for 15 years.
As recommended on Pembleton forum I reused the original Citroen nylon fuel pipe as apparently more durable than modern replacements, however on introducing modern fuels pipe grew in length!
This led to a kink in pipe cutting fuel off on first trip out,this was eased however pipe continued to grow leading to comments at MSVA, again bends were eased. Pipe continued to grow.
Having now been in use for 6 months i think pipe is stable so yesterday I drilled out the rivets holding the rubber lined pipe clips removing all the kinks and refitted, pipe is now 2" longer than when fitted!

Carb Problem Solved
Previously my carb has flooded slightly on a closed throttle, now does not.
My theory is that pump was having to suck hard to overcome kink and pushing too much pressure into carb.

Could be related to your problem, as you car has been standing, if not might still be useful for others.
Suggest if anyone is building a special from a donor that has been standing for years that they soak nylon pipe in a container of petrol before fitting (or use copper pipe).

Jack
Pembleton Super Sport "Mon Petite"

[Rocketman1955]

Check carefully where the fuel leak is coming from. I have been investigating why my car misfires at light throttle after changing up gears. (a separate post) Carb is a 26/18.
My first thought was the accelerater pump not working. Having removed the air cleaner and manually operated the pump lever I could see good squirts of fuel going into the carb.. So accel. pump was ok.
Shortly afterwards there was petrol running down the side of the crank case.
Initially I thought a carb. gasket was leaking or the fuel was coming out of a butterfly spindle as the engine was not running.
However, on closer inspection it was coming out of the intake manifold underneath where the 2 intake branches meet.

Looking closely I could see a short hairline crack under the intake manifold .
The crack is small, but will allow some air ingress which may cause the engine to run lean at light loads.
However, the engine idles perfectly, spark plugs have good colour and the engine never smells of petrol when it is running!
Obviously this needs fixing, but I have yet to establish if it is contributing to my driveability issue.

[2HP]

Thanks folks. In an attempt to eliminate pump and tank-to-pump issues from the equation (confusion) I rigged up temporary gravity fed tank.

Made a new gasket from 0.5mm paper fit for 300c.

Then tried two different carbs :

[1] First was a 26/35 CSIC of unknown provenance . Engine starts and idles well though increasing the revs is bloody awful - Terrible spluttering hesitation, then when revs are up it sits at high revs ok, but when foot off throttle it takes 20 seconds for the revs to fall - almost like a sticky cable (though it isn't a sticky cable). On closer inspection, operating the throttle delivers only a series of drips from the pump injector (rather than a neat squirt) and a lot of fuel dribbling from the where the injector emerges from the carb body, so I am guessing perhaps the pump injector seal is shot?

[2] Then tried the original carb again, the 24/21. It starts and runs really well, and throttle works well too, but fuel still weeping heavily from around the carb to manifold gasket region. Given there was new paper gasket which worked on the first carb, dried the fuel off a few times , only for further weeping to reappear, even when engine not running. suspect it may be leaking on both sides where the throttle spindle enters/exits the carb body?

Now I'm wondering which of the two carbs will be easier to repair? Do the 26/35 gasket kits provide a replacement injector seal?

Any ideas what the cause of the leaking on the 24/21 might be? Could it just be the float needle? Can fuel leak from the throttle spinde?

All advice gratefully received!

thanks

[Vyv Cox]

My unheated manifold also leaks fuel on startup, immediately beneath the carburettor on the underside of the cross tube. Inspection with a mirror suggests it to be a drilled hole rather than a crack.
When I was having misfire problems I thought this drilling might be the cause but running with tape over it made absolutely no difference.

[cmwbob]

the small hole in base of manifold is to allow escape of excess neat fuel from over enthusiastic use of the eccelerator pump.

[Jack602]

I am not sure that a gravity feed will give accurate results as the carb is designed for 3psi, gravity feed carbs use different float needles.

Might be worth checking fuel pressure, I had the bizarre problem of carb flooding after I switched off engine (easy to spot on a Pembleton).
I checked fuel pressure (new pump) it was 5 psi rather than the recommended 3 psi, so I made a thicker pump to engine gasket (you can buy these from Der Franzose). Tested now 4 psi and no flooding but carb too weak on tick over.
A 0 to 15psi fuel gauge is less than £3 on e Bay including delivery from China, a 1/4 BSP to 6mm adapter is another 99p (I had an adapter in stock), at these prices worth testing pressure to see if is too high or too low.

Jack
Pembleton Super Sport

[2HP]

Dear Forum People

Thanks for all the various pointers. After much head scratching I've now got a carb that works well and in hindsight I had to address several problems, not least my lack of experience ! I'm sure to most lomax folk these would have been immediately obvious, but to a relative layman like me ended up being a great, albeit frustrating, learning experience!

If you're inexperienced like me and struggling with an old carb and a car that's been lying idle for ages then I hope some of this may be of help:

I decided to try and fix the newer carb, i.e. the 18-26 variant of the 26/35 carb rather than tackle the awful fuel leak on the older 21-24 variant of the 26/35 carb. My reckoning was that the older carb (21-24) looked badly abused and spares, gaskets etc might be easier to obtain for the newer carb. The newer carb (18-16) looked great and idled beautifully, but had a monster flat/dead spot with terrible backfiring (actually 'front firing' through the carb) which occurred almost immediately after the throttle was opened, & which stalled the engine unless I moved the throttle very quickly to fully open position (allowing the secondary jet etc to take over). With both carbs the exhaust stank terribly.

A good proportion of the terrible exhaust stink I believe was due to the dregs of stale fuel in the tank. Initially I thought I'd drained the tank (a lomax SS affair), but it appears one cannot fully drain the thing. So, when I initially added only a gallon of fresh petrol, the fresh fuel was contaminated to some extent by the leftover 'turpentine-like' dregs - Lesson here, with a car that's been left for years, is to ensure the old fuel is either fully drained away or very well diluted by a full load of fresh fuel.

Another sizeable portion of the exhaust stink I believe was oil seeping into the barrels - I had rebuilt the heads ten years ago (to replace a cracked valve), in the course of which I had accidentally broken a ring and ended up replacing the rings on both pistons. The engine was not run in after this, and whilst I had at the time ‘busted’ (dulled) the glaze on the pistons, I think I'd replaced the oil with synthetic 10W40 – Seemingly one should generally use mineral oil during a running in period because synth is too slippery and a little friction is needed to help the rings bed (wear) in - Therefore, to try to eliminate burning oil from the stink mystery, I changed the oil to cheapo mineral 20W50 - This resolved most of the remaining exhaust stink.

Still persevering with the newer 18-26 carb, the next problem was that operating the throttle did not result in petrol squirting into the primary choke from the throttle injector. Bubbles were however visible just where the injector emerged into view – I removed the injector and fitted a new rubber O ring and this fixed the injection problem. Whilst a slight improvement overall, I’d say 90% of the dead spot when opening the throttle was still there, and nowhere near making the car driveable. Fixing the injector leak certainly delayed the dead spot by a fraction of second, but did not come close to fixing it.

I then cleaned out all the internal jets and found a fair bit of crud in the emulsion tube which feeds the primary - Alas to no avail & this had no effect on the mega flat spot (incl backfiring through the carb) - Still happening just as the throttle was opened.
I stumbled on a post in a bikers’ forum which stated that backfiring through the carb is a classic symptom of weak mixture. So I knew I was still looking for something letting too much air in and/or a restriction in the fuel supply.

The secondary butterfly did not look like it was 100% fully closed at idle, and so could be weakening the mix, so snipped the plastic seal off the stop for the secondary throttle and backed it off a turn - This closed the hole in the secondary better at idle. This did help improve things ever so slightly, but still most of the mega flat spot and backfiring remained.

Thinking ‘air leaks’, I removed the 'choke pull-off device' from the carb lid and fitted a blanking plate over the hole - No improvement.

Thinking ‘restricted fuel supply’ I borrowed the main jet off the older carb (the 21-24 carb, which is a 120 size jet) and tried this in place of the main jet on the newer carb (which is a 102.5 size). This helped quite a bit to reduce the awfulness of the dead spot but it was still not anywhere near driveable & made the exhaust a little stinky again. So, back in with the original 102.5 main jet and more head scratching.

FINALLY THE MAIN CULPRIT FOUND: After a fortnight of intermittent effort, including taking carbs on and off over a dozen times, & just about to give up and raid the family silver to purchase a recon carb from Burton, I stumbled upon one of Ken's posts on the old CSC forum. Here Ken mentioned the ‘rare occurrence of a throttle linkage seizing’, i.e., the mechanism which connects the primary and secondary throttles. I ignored this at first because I could see the secondary throttle opening slightly after the first, and assumed (incorrectly) at the time that the linkage was not seized. However, the second throttle is only meant to open only after the first butterly is open perhaps 45 degrees, whereas here the second throttle was opening when the first was only slightly open.

Freed up the throttle linkage and low and behold the terrible dead spot is gone. I guess I owe Ken several pints for that one!

I will take a pic and post it up here later showing where the linkage had been seized..