Austin Big Seven starting problem

[Thowdfella]

As I said in the beginning I am using fresh fuel - I have just had the tank out and fully cleaned and treated and replaced the fuel line as well. I am also using a new set of plugs. I read a very good article today on Zenith carbs and it explained how they actually work. Under starting from cold it said the strangler would be fully closed AND THE STRANGLER VALVE!  I didn't know there was one but when I looked at the "strangler" or choke, it was fully closed BUT the valve was stuck open. When I dismantled the choke the valve broke off so I am now awaiting a new one. I would like to think that this is the problem but will wait and see. There seems to be doubt as to whether there should be a strangler valve on my carb but it does show one in the drawings for that carb

[john williams]

There is a little confusion here with carburettor terminology. The "Choke" is the reduction in diameter in the main inlet section of the "carb". On Zenith carbs this choke size is a fixed diameter. The cold starting device, commonly, but incorrectly called the "choke", is actually the "strangler valve". This is the flap on the inlet of the "carb" which is operated by pulling out the "cold start" cable. Again incorrectly called the choke cable. On early Zenith "carbs" the the cold start flap was fixed solidly to the operating lever. This caused a problem when the engine started, as the engine could not draw enough air to form a mixture as the throttle is opened. Common parlance "Over Choking". On later "carbs" the cold start flap valve is spring loaded, it closes in the same way as the early "carbs when the cable is operated, but the spring loading, allows it to open  automatically when the throttle is opened. It sometimes happens that the spring closing of the cold start "strangler valve" fails. Thus the cable and strangler valve lever operate normally, but the strangler valve flap sticks in the open position. Easily cure with penetrating fluid on the strangler valve shaft.  Check that with the cold start cable fully out, the strangler valve is fully closed. Then apply finger pressure to the flap valve, it should open easily without moving the cable operating lever. If it is difficult to move, it would seem you have the early type of "carb" which is prone to "over choking". However, even with these early carbs, the engine usually starts easily, but will not rev freely, and eventually the engine stalls as the spark plugs become soaked. I hope there is enough information to guide you to a successful solving of your problem, but at the very least it should clarify some of the carburettor terminology.

[Colin]

I have mentioned this problem before but never managed to sort out the problem. The carb is a Zenith vm-4 which appears to be in good condition with no worn spindles. It has now got to the state where it will not start at all. I have done a valve grind; there is no sideways movement on the pistons; the compressions are all around 70 when turning the engine over on the starter motor; the timing has been checked again and again and ignition laser indicators on the plugs are all  flashing. When the head was off we checked the camshaft timing which appeared to be correct. but still wont start. Last night when I was doing a last ditch attempt to start it - I forgot to turn the ignition switch on. When I did turn it on and tried it - it eventually kicked into life!
To me this suggests petrol starvation so its back to the carb. on previous occasions when it wouldn't start, I have removed the float chamber - filled it to a higher level than what was in there and then it started. Can anyone help / I am using fresh fuel and priming with the fuel pump lever and its a new pump which gushes fuel out .

Big Sevens hate old fuel!!
Try pouring a little fresh gas into the carb while cranking and ignition on.

[Thowdfella]

Thanks for that Tony. Yes all around 70 but that's just on the starter motor and maybe before the oil is fully circulating.  From what I remember in my youth they should be 14.7 times the compression ratio which is 6/1 so should be 84 on a perfect engine when running. Even if a bit low, they should fire at that I would have thought.

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Thanks for that John - you are right, we do get mixed up in using the correct terminology. In my case, The strangler valve is a very thin piece of spring steel which should be closed with the engine stopped but which the suction from the engine sucks it open when running. When you take the strangler off the shaft and turn it over, there is a guide post around a cut out in the strangler valve and it was fouling on it and so stuck open. when I tried to free it it broke in two so now I have a much bigger hole!
I am struggling to find a replacement so can I just seal the "hole" by aralditing a circle of metal over it? As I understand it - later versions had a solid brass strangler anyway. I would have liked to add a photo but cannot find a way of doing it.Does anyone know how to do it

[Nick Salmon]

Stale fuel is my pet bete noir. How I crave a dose of leaded 4 star that would stay good for months and months on end!

Point is this - I too had a fuel tank out, cleaned and sealed. Put in fresh fuel straight from the pump. Car ran fine. Went back to it again about six weeks later and it would not start. Put newer 'fresh fuel' into the float bowl and it fired up immediately. Next day - same thing. This is on an RP saloon by the way.

So I drained the tank and refueled it. All ran fine and with regular use is continuing to run fine..

I put the drained fuel in my MGB and although it would start, it ran like an utter pig.

This is not the first time fuel I have had fuel go off in a relatively short period. Perhaps it is atmospherics. Perhaps it is ethanol causing it.

So now, whenever I get a problem with starting a car that has been standing for more than a very few weeks, and the cause isn't obvious, I always begin the hunt by using absolutely fresh fuel in the float bowl. This has solved the problem more times than not.

[Thowdfella]

Stale fuel is my pet bete noir. How I crave a dose of leaded 4 star that would stay good for months and months on end!

Point is this - I too had a fuel tank out, cleaned and sealed. Put in fresh fuel straight from the pump. Car ran fine. Went back to it again about six weeks later and it would not start. Put newer 'fresh fuel' into the float bowl and it fired up immediately. Next day - same thing. This is on an RP saloon by the way.

So I drained the tank and refueled it. All ran fine and with regular use is continuing to run fine..

I put the drained fuel in my MGB and although it would start, it ran like an utter pig.

This is not the first time fuel I have had fuel go off in a relatively short period. Perhaps it is atmospherics. Perhaps it is ethanol causing it.

So now, whenever I get a problem with starting a car that has been standing for more than a very few weeks, and the cause isn't obvious, I always begin the hunt by using absolutely fresh fuel in the float bowl. This has solved the problem more times than not.

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Finally this is the end of this Saga. Got a similar carburettor off eBay and stripped and cleaned it. No different got a new distributor head and rotor arm - no different. I have been listening to all the comments re fuel and have filled the float chamber with fuel but still wouldn't start.
Yesterday I got new fuel in a container at Morrisons and rigged up a pipe from the pump inlet into it and the car started. Again this morning - it started no problem.
The fuel I was using previously was less than three weeks old but it won't start on it. I have been advised to use super unleaded - I believe Tesco has one at 99 octane and this doesn't deteriorate. Can't quite believe that but at least it's starting from a higher level!!

[Dave Wheatley]

I've always been a bit sceptical about the stale fuel argument, so after reading this thread, I de-winterised my 1931 tourer, and started it using the approx. 1 gallon of fuel that had been in since last November.
Started and ran OK. As far as I can remember it was common or garden unleaded from the local garage.
Go figure (I've always wanted to use that phrase, and it seems appropriate here!)
Dave

[Reckless Rat]

More and more garages are no longer selling straight unleaded fuel, but predominantly E10. Whilst an A7 should run on virtually anything, the best alternative is Super unleaded 98 octane without ethanol. I dont use lead substitute additive. 

I must admit I have never had any problems with fuel ageing, but it obviously exists. Now you've got the car running, do another compression test with the engine properly warmed through & throttle open. 70psi seems low to me. My RP saloon with 37 head gives 125psi hot.

[Michael]

Does fuel go 'stale' as a result of having a considerable surface exposed to a large volume of air? In other words a full tank or container would stay 'fresh' when a half empty one would go stale?

Many of us (but not all) leave our lawnmowers over winter with a half empty tank and many of us start them up easily in the spring. Others find they need to drain the carb.

I have an outboard motor that I will religiously run till the carb is dry when I know I am going to leave it for a few days. I try to keep tanks full. Have never had a problem as a result.

Never had a problem with the RP.

It would be interesting to know the science.

[Steve Jones]

I, too, have never had a problem with so called 'stale' fuel. I understand that ethanol does take in a degree of air born moisture over time but as yet, this has not caused me issues. I took my RM Saloon out on Monday afternoon. The first time it's been on the road for two years. The half tank of petrol in it is also two years old and is normal unleaded. It started first time and ran perfectly. 'Stale' or not, no issue there. The engine is perfectly standard with no go-faster modifications but is in good condition. I'm not alone in having the view that 'stale' petrol is blamed when the real issue is some other weakness in the engine or its systems. In the case of the Big 7, 70psi compression seems very low and I'd suggest that's more of the issue than the fuel being 3 weeks old. Yes, of course fuel will deteriorate over time but the deterioration over 3 weeks shouldn't make any difference.

In another place, Esso Super Unleaded is reported as having no ethanol in it at most UK outlets. It's what I use in my two competition Sevens but that's more a product of it being sold at my nearest petrol station than anything else.

Steve