Hi to all,
As a new A7 owner, it was a big day for me yesterday when I went on my first long drive of some 126 miles!

Only two problems occured both to do with fuel.

1. After the run out, petrol leaked out of the breather hole in the top of Zenith 22FZ bronze carb every time I turned on the fuel tap and dripped close to the exhaust pipe. Thinking I might have too much fuel in the tank causing a higher pressure at the carb, I drained some out-no luck.

2. Running with half tank or less, I made a wrong turn and negotiated a steep long hill with bends! The car coughed and died. There was not enough petrol and it was not coming out the pipe, it was all at the back of the tank! Turned back down the hill stalled again so filled up from a gallon can, ran fine after that.

I have a lot to learn about bygone motoring, but advice on the carb would be very useful.

Many thanks.

Chris

PS Have learnt not to steer and break at the same time with cable brakes!

I am also new to A7 motoring, yet to enjoy my first drive tho, this should happen next week. Mental note to myself, avoid steep hills. Is this the reason drivers used to reverse up hills? Which A7 varient do you own?

Hi David,

I have a 1931 RM Saloon.
I think they went up backwards as reverse is a lower? ratio than first, but it may have been to do with fuel as well!
I should have said one shouldnt turn whist braking as it pulls to one side and makes a clonking sound which I can only think is the pulling on one side harder than the other when the cable is tight!!

Which A7 is yours?

Regards

Chris

Hello Chris.

Please be assurred that you can drive a gravity fed Austin Seven with a full tank of fuel.

You obviously have a problem with the float valve in the carby not shutting off properly.

This could be due to there being dirt in the needle valve, or else the needle valve itself is worn or maybe needs the collar adjusting. It could also be that your float might be leaking.

There is, I think, a very good article on Mike Whittome's Solent Web site which goes into some detail on this subject.

Have a look at:
http://www.windling.demon.co.uk/SolentA7/technical.htm

If you can beg, borrow or buy a copy of David Woodrow's "The Austin Seven Manual" that has some helpful info as well. Don't purchase off Ebay though, they seem to go for absolutely expensive prices there. They are still available through the publishers, but I can immediately give you contact details. I am certain someone else will be able to.

Best regards

Barry R

Chris,

Publishers of 'The Austin Seven Manual' by Doug Woodrow that Barry mentions:

Mercury Vintage Services
Rosedale, Station Road
EMNETH
Norfolk PE14 8DL

Email: woodrow@mercuryvintage.freeserve.co.uk

Jeff

Jeff, I run with a piece of asbestos matt (acquired before all of the who haa, though quite justifiable) fixed around the downpipe with wire for about 9 inches directly under the carb. Apart from saving your car from bursting into flames (many have) its useful when you have to remove the jets with a hot pipe. I expect a modern equivalent can be purchased. A very necessary mod in my view.

Thanks for your help,
I have a copy of the Woodrow manual but it doesnt go into much detail regarding levels and floats.
I have looked at the Solent Owners site which is great for setting petrol levels but i am not sure what shuts off the fuel in the first place. It seems that when the car is cold and I leave the tap on, fuel leaks through the air inlet but when it ran for a long time it comes out the breather hole!
The idea of the asbestos bandage is good,I will at least try this.
The top of the carb. is 'welded' to the bronze body and it looks as if it has been attacked by a pair of stilsons at some time. I guess this is why the aluminium 'manhole covers' are sold now!

Thanks again and sorry to be a pain.

Regards

Chris

Chris,

Don’t worry about “being a pain” - we Austineers are a masochistic lot and enjoy it!

If you have a look at the two thumbnails below, you will find two sectioned drawings of Zenith updraft carbies.

The one which is actaully labelled Austin Seven is a bit fuzzy, but I think it will serve the purpose.

In essence(no pun intended), your petrol is fed via the pipe from the tap into the bottom of the carburetter, from whence it flows to the bottom area under the fuel bowl, courtesy of and in obedience with, Mr Newton's well known laws of gravity. (Through the "Strainer" which is depicted somewhat unclearly on the drawing)There is a “valve and seat” at the bottom of the fuel bowl which is provided for the express purpose of maintaining a set full level in the bowl.

This is normally referred to as a "needle" valve, and as you will see from the drawing, it is comprised of the "doodad" which looks a bit like a nail, and which pokes up out of the fuel bowl cover (the "tickler"), and which is ground to a point at the bottom end. This needle had a small ring "collar" around its upper end inside the fuel bowl, which is coupled up to a pair of counterweights. If you now look at the second clearer drawing of "Zenith Carburetter in Section" you will, I think, quite clearly get the idea. This second drawing is not exactly the same as the 22FZ but is near enough for purposes of understanding the operation of the float area.

When there is no fuel in the bowl, the float will sit on the bottom and the counterweights will droop down, lifting the needle off its seat, allowing petrol to flow through the "float needle seating" and into the float bowl. The float will then rise with the petrol (that is why it is called a float) and a point will be reached where it will lift the drooping counterweights until such time as their upwards movement forces the needle shaft down, via the ringed collar, hard into the needle valve seat, shutting off the flow of further fuel into the bowl.

The point at which this shutting off action occurs, must be carefully set. If it is too low, the carburetter will starve of petrol and if it is too high, the carburetter will flood, and petrol will find its way into the choke tube, onto you hot exhaust pipe with all the resultant dire consequences you are now experiencing.

So, the long answer to your short question is in the above. You must get your needle and valve shutting off at the correct fuel level point in the bowl. The Hon Mike Whittome;s excellent exposition on the "Solent" site should guide you to a state of drip free carburetter and safety.

If your car has been previously behaving itself in this department, you may just have some grot in the needle valve area which is preventing the valve shutting off properly.

Please keep us all informed on your further adventures

Regards


Barry R.

Hi Barry,
Thankyou so much for your time. The explanation makes it very clear now.
Does the needle lift from the seat due to the pressure of fuel or does the counterbalance weight force the collar upwards? Is the collar fixed to the needle and is this the item that needs to be set at the right position and soldered in place? The 3mm fuel clearance mentioned in Mikes explanation, is this 3mm below the manhole cover?

Many thanks again for your time

Chris

Hello again Chris,

After I re-read my explanation I must confess to thinking that I really did not explain the float action properly.

If you consider the situation with a "dry" bowl.

The float will be resting on the bottom of the bowl, and the outside ends of the counterweights will be drooping downwards.

The downwards drooping will cause the inner ends of the counterweights to lift the collar, which is fixed to the needle. The needle will therefore move "upwards", moving the tapered end off the needle valve seat.

In that situation, then, the needle valve will be "open."

If we then turn on the fuel supply tap, fuel will enter the opened needle valve, and commence to fill up the bowl with petrol.

As the fuel level rises, so does the float, pushing up the outside ends of the counterweights, until the point is reached where the inner ends of the counterweights will move the collar, and thus the needle valve pin downwards, until the valve "shuts off."

This point off shut off must be carefully arranged to be at a point where the fuel in the bowl is approx 3mm below the top orifice in the idling jet.

Adjustment of the level is effected by moving the collar up or down the needle pin.

You are correct in stating that it is the collar which is secured to the needle pin by solder.

As you can probably visualise, the movement of the needle pin up and down will occur continuously as fuel is drawn from the float bowl as it is consumed by the running engine.

The float will sink lower in the bowl as fuel is consumed, thus reopening the needle valve, readmitting more fuel to the bowl. The float will again rise, eventually closing the inlet valve when the pre-determined level of fuel in the bowl is reached.

I don't really know where you are situated in UK in respect to Mike Whittome, but am certain that he or for that matter one of the many other A7 Guru's who you must be surrounded by would be happy to give you close at hand, if not "hands on" assistance.

Getting the right fuel level is very important and can actually make a considerable difference to both the convenience and performance of the car.

I must confess that I get all "dyslectic" each time I have occaision to adjust the collar to get the fuel level right, but it is really only a matter of logic to work out whether you need to drive the collar "up" or "down" the needle shaft.

Stick with it. It is good to see new folk entering the wonderful world of Austin Sevens.

Regards


Barry R.

.

Hi Chris,

I thought I had better contribute to this thread after all Barry's comments!

The infamous three millimetres which we are seeking are in fact the distance of the fuel level below the top edge of the 'main jet cover'.

I have repeated one of the previous pictures here so that you can see it a little larger. Also added an arrow pointing to the appropriate bit.

As you can see the main jet has been removed (standing on the left), and a dummy tank connected to the float chamber via a flexible pipe. When the tank (pop bottle) is raised above the carb the level in the jet cover should stabilize 3mm down from the top – just visible down through the hole.

To answer your other question: At rest and with empty float chamber the float falls to the bottom of the chamber and thus is no longer pressing upwards on the counter-balance weights. The weights hang down and thus lever the needle upwards opening the intake jet.

When the fuel enters it ‘floats’ the float which rises up, finally taking the weights with it. Now the needle is levered downwards, and the point seals (hopefully) the intake jet.

It is at this point, as the needle closes the hole, that the level in the chamber and the main jet cover should settle at 3mm down.

When this is achieved carefully remove the needle and, without moving it, solder the ‘bobbin’ in position. It is best to tin the bobbin and the needle prior to masking the adjustments so that copious blobs of solder do not alter the weight!!!

Mike

.

Sorry Barry,

Did not mean to take wind from your sails. As you will see from the timing we were both hitting the keys at the same time.

And Chris,

Yes, of course, if I can be of help ..........

I live in Andover to the North of Hampshire.

Mike

Chris,

Sorry about this.

What I should add in response to your latest question is that the 3mm does not refer to the "level below the manhole" as you so delightfully put it.

If you have a look at the clearer of the two illustrations I posted earlier you will see the general idea (remember that this particular illustration is not actually of the 22FZ carburetter, but will suffice for purposes of illustration).

You will see that there is horizontal "hatching" in the diagram denoting fuel in the bowl. You will also notice that this fuel level is shown to be about 3/4 the way up the float. If you look across the illustration to the left, you will see a representation of the main jet and the idling jet.

You will then see that the fuel level is depicted as being just below the orifice in the tip of the main jet and the idling jet. This is where the 3mm applies.

If you think about it, if that were not arranged to be the case, then petrol would drip out of the main jet, for example, into the choke tube and eventually out of the carby and all over the place, paricularly when the engine was stationary with the fuel tap "on".

Almost certainly, that is the situation with your particular present dilemma.

The "Solent" site gives succint details on how to get the level right, although it is written specifically for a 22FZB carburetter, the principles remain the same.

I hope the above is further clarification and not complication of your question/s


regards


Barry R.

Hello Mike,

I have barely enough puff these days to breathe, let alone fill any sails.

I just found that I was starting to get tongue tied.

I really should write up resonses in Word and then transfer to the Forum.

Your description of "below the main jet cover" is of course the most succinct way of putting it, but I just couln't find the words.

regards

Barry R.

Thank you all so much for your time helping me out.
The carb will come off tonight, I know how to do this since it came off a month ago when the butterfly screw came out and disappeared somewhere!
The job will be getting the 'manhole cover' off but if I soak it I might be lucky, or its a new one!

I think I have been lucky not to have a fire with the petrol that has been leaking out onto hot exhaust pipe!

I will keep you informed with my findings.

Many many thanks

Chris

Someone mentioned "manhole covers" --I assume to be covers for the float chamber. Can someone tell me where I can obtain such a replacement.

Ken asked:

> ... covers for the float chamber. Can someone tell me where I can obtain such a replacement.

I think Tony Leslie (Holmesdale Sevens) sells them - he's on +44 1424 830730.

David

Willie McKenzie (please interpret/forgive my poor spelling) lists them in his catalogue

Hi All,
Update time!
Carb came off last night and the manhole cover came off without too much trouble with a pair of waterpump pliers (I too might need a new one soon!)

What I found was a counterbalance weight and a brass fixing pin sitting on the top of the float!!
The other weight and pin were only just connected.
It was obvious that the extra weight on the float along with the obstruction above the weight would have stopped any form of petrol level control. Likewise, the needle valve could not have been opened by the remaining weight either.
How I ever ran for the past 500 miles with this arrangement I do not know. The car sounded fine although I have had the petrol leakage problem.

Tonight the carb goes back on the car, and I will see if any adjustments will have to be made!

Again thanks to all for the expert help, I will post again following recommission.

Best Regards

Chris

Hi there again,

OK, carb is on and no leaks at all. Its so good to drive without a smell of petrol. I thought this was normal!!

The car runs much better now, pulls when asked which it didn't do before.

As a matter of interest, I made some new pins for locating the weights under the carb. lid with 1/16inch brass brazing rod which I squashed at each end in the vice and dressed with a needle file. This was very successful.

Again thank you for your help, I will stick the posts in my 'Log Book' for later reference then maybe I can help someone else in distress.

Best Regards

Chris

Congratulations Chris,

You are well on the way to becoming a well seasoned Austineer.

At the risk of being seen to be trying and teach you how to suck eggs, or otherwise insulting your intelligence, don't rely on your needle valve and seat to keep the petrol tank "turned off" when the car is idle. Always turn the petrol off at the tap when leaving the car.

Best regards

Barry R.

Hi Barry,

Thanks for the very sound advice. I will indeed keep petrol tap shut!

I will bring the car to work tomorrow and drive round the country lanes of Surrey as the weather is set fair.

I have a lenghthy list starting of jobs to do over winter on the A7!

Very Best Regards

Chris

Turning off the petrol tap can be seen as an additional security device as well if like me the car has no key. (Could even fit a little padlock to it if so desired.)