DDK - Die Deutschen Klassiker

Some years ago I replaced the top gaskets on the float bowls on my Zeniths each secured by the 6 screw headed bolts. Simple job no problem the tops sit above the floats by a fair amount so no chance really of fuel leaking unless with faults with floats or the needlevalve that controls fuel into the float chamber.
Then with Ethanol in fuel I noticed hot starting never a problem but cold starting if the car was left say for one week became really bad. It meant spinning the motor over for 25 seconds then depressing the accelerator 5 times to give some squirts from the Zenith jets. I looked everywhere for leaks nothing to see, in the end I just put up with it until a week ago! I looked carefully at the join between the float chamber top and carb body. I saw a brown line along it. I cleaned it and tried with a 8mm spanner to see if the top was loose. Each bolt could be turned 1/2 turn !! I did the same with the other carb same correction so the once new gaskets had lost compression.

I then waited one week till today I pulled the car out from the garage turned the fuel on depressed the clutch, turned the ignition on pressed the accelerator 3 times and turned the key to start. Immediate start up !!! Perfect starting after so many years of annoyance. REASON there must have been a gap between the body , gasket and float chamber top. It allowed air in to evaporate the fuel in the bowl.

To say I was happy would be an understatement. I could always get it going but what if someone else tried at some point !
I tell you this story just in case you have a similar problem and could not solve it just like me.

Roy

Hi Roy, I run a B on zenith 32 carbs and experience the same cold start problems as you say, over several year’s trying to nail down the cause I have come to the following conclusions.
The zenith carbs are a leaky old thing, they work well when setup correctly but if you consider the age of them and the gaps inherent in them for fuel to escape ( shaft holes, lid not sealing and breather in Ventura), modern fuel just wants to escape and can do so fairly easily. So if a hot engine is left to cool and not used for several days more often then not the carbs lose petrol to the atmosphere, I have concluded that this makes starting the engine from cold difficult because the carbs have first to refill and then the accelerator piston skirt has to get wet to make it flexible to form a seal with the cylinder wall so as to push out fuel into the Ventura and into the engine, thus making the engine start. The Achilles Heal of the 32 carb is the leather skirt that provides the seal on the accelerator pump, it dries out very quickly and when it does it doesn’t provide a good enough seal to push out fuel from the accelerator nozzles that make starting easier.

To overcome this I have installed a low pressure auxiliary electric fuel pump ( 6 volt) into the fuel line after the the stop cock ( underneath the passenger floorboard) which I switch on for 30 seconds to fill the carbs before starting the engine, this doesn’t adversely affect the engine fuel pump in any way. If the car has been standing for sometime I wait a few minutes after filling the carbs, pump the accelerator 4 or 5 times and the engine will start on the first or second time, the electric pump is switched off when the engine starts and off we go,the starting of the engine when warm is easily done by adopting a part throttle pedal.
I have spent a lot of time trying to find an answer to the cold starting on a 356 and concluded as above the main problem is the leather on the acceleration pump, I have discovered that zenith made a 36 Ndix carb that is almost Identical to the 32 and that has a rubber skirt on its pump, the pump cylinder is the same diameter but the piston itself is not the same length as the 32. After much sleuthing I managed to get hold of the rubber skirts from the states and have fitted a pair to a spare set of 32 pistons and I have been assured they are compatible with ethanol fuel. I have as yet to change them for my existing carb pistons but when I do I will be interested to see if my theory about the leather skirts is true. Leather skiers on left , rubber skirt on shaft , right

Thanks a lot for those comments about the Zenith 32NDIX carbs. Yes you are correct they need to be looked after to get the best results. After buying my car in the 60's the years rolled by really without carb problems. I bought a syncrometer to get them balanced and all went well till first of all the rubber gasket that covers the idle and main jet failed and wow it took me some time to evaluate that. Petrol leaked down and I thought the main gasket to manifold was the problem so when I bought two new ones, and the rebuild kit gasket set which included the jet cover gasket and accelerator pump. Checking this was over 20 years ago!! How time flies by !! So back then before stripping each carb I checked the accelerator pumps were delivering the correct volume of squirts from the gas pedal. They were to spec which surprised me.

So after the work they just ran and ran fine till I think this Ethanol addition to fuel. Or that is what I thought !! If fuel loss can be seen its so much easier to understand what is happening. I even today buy Esso supreme as it did say Ethanol was used to the minimum. So to at least find a gasket sealing the carb bowls obviously looser than it should be, getting the immediate positive cold start the same as 55 years ago just made my day or even year!

Your thoughts about rubber instead of leather on the accelerator pump is valid I have wondered a lot about those over all the years I have had my car. I believe from memory of my receipts the previous owner did have them rebuilt in the mid sixties but at present they are same as when I bought it from him. I still have the new one in my spares box never used.

Roy

I had the same problem and much worse if I didn’t use the car for a couple of weeks.

Eventually I discovered that the accelerator problem pumps had leather diaphragms which were drying out and needed to be soaked in petrol before they worked well enough to start the engine.

The engine came out when I had the body restored so I removed the heads, barrels and pistons and found I had a 1720cc engine with the counterbalanced crank and that some rings were broken and bores were scored.

The heads were superb, so I replaced the barrels and pistons and fitted Solex manifolds and bought Chinese Solexes because with rubber pump diaphragms.

I had a steep learning curve to setting them up properly and re-jetting them for 1720 cc, but I was worth it. Starting is slow and reliable but better with the more expensive fuel with less ethanol and performance right through the range is noticeably better. Just feels more eager.

So now I have a spare 1720 SC engine I built that’s complete and running and a 1720 cc C engine in the car.

Hopefully I’ll never need the spare.

I am glad you got such a long standing problem resolved Roy.
It will make the thought of using the car that much better, knowing it will start without a big effort. And thanks for the advice.

Karl.

Well done for solving this problem. However, if my car has been sitting for a while I would prefer that it didn't start first time. I always try to spin the engine for a bit using the starter, with no pumps of the accelerator, in hope this spreads some oil into the engine before it starts spinning at 1000+ rpm

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Yes Neil correct its better to have a few turn over revolutions from the starter when cold. I use the starter now so it does turn it over for a short time say around 4 seconds then I give the gas pedal 2 presses and it fires up fine. In Winter maybe it might be 3 presses I have yet to establish that.
Warm engine it starts without any fuss at all.

Roy