A40 Somerset fuel drain back.

[charlie-farlie]

Hi folks.

The fuel on my Somerset drains back to the tank if the car has been standing for more than two or three days, resulting in the need to crank the engine over for anything up to 20 seconds to get fuel back to the carb and the engine to start. I rebuilt  the original fuel pump to no avail, so I got a second hand fuel pump and rebuilt that, again to no avail. I have checked all fuel lines and connections and I have even tried removing the locking petrol cap and fitting the standard cap. Again, to no avail. I have also rebuilt the carb. If anyone could throw some light on this for me, I would be most grateful.

Many thanks.

Robin

[charlie-farlie]

Hi Dave

Many thanks for your reply. I didn’t actually rebuild the carb myself. I sent it away and had it rebuilt by a specialist. I didn’t consider the carburettor because the car has had this fault since we bought it three years ago.  I recently purchased a box of carbs, rebuild kits,  gaskets and a large box of other  pieces from a former Somerset owner, so rather than mess about sending the carburettor back to the company who rebuilt it, I will replace the emulsion block gasket myself and see what happens.

Thanks again for your help and advice.

Robin

[charlie-farlie]

Hi Dave,

Many thanks for your reply.

I have several emulsion blocks so I will do exactly as you suggest. Strangely enough, I always tighten all nuts, bolts and screws a little at a time, just like I would a cylinder head. I will (hopefully) be doing this job tomorrow. It is so strange how I have tried three carbs on this car and none, including the specialist rebuilt carb cured the problem, which is why I tried the pump.

When I rebuilt the petrol pump, I had to stretch the diaphragm slightly to make it fit. I then pumped paraffin through it as recommended in the service manual.

I will post my findings on the forum once I have taken the action you have recommended.

Thanks again Dave.

Kindest regards

Robin

 

[charlie-farlie]

Hi again Dave.

I have tried everything that you have suggested. I replaced the emulsion block with one that has a super smooth surface and fitted a new gasket yesterday (Thursday) morning. Prior to starting the car this afternoon, I took the top and filter off the fuel pump and there was fuel in the bowl. I pulled the starter and it took 9 seconds for the fuel to fill the carb and the engine to start. I think that I will have  to search for a new/old stock carburettor over the winter as despite having this carb professionally overhauled, it is clearly not performing as it should do.

On the advice of Graham, I am taking the head off over winter in an attempt to cure long term poor running and to stop the number three plug from sooting up.  I still have the torque down instructions that you gave to me over three years ago when I spoke to you regarding poor running. Over this winter, I am HOPING to make this car run as it should do for the first time in my ownership!

Thanks for all your help.

Kindest regards

Robin

[charlie-farlie]

Hi Dave.

The instructions that you have just provided are pretty much what I did when I rebuilt the pump. It pumps through with the primer lever perfectly and doesn’t appear to be a problem in service. However, I have another pump and a couple of new repair kits in a box of items that I purchased from a former Somerset owner. I will rebuild another pump later today, following your advice to the letter and will fit it to the car and see what happens. We’ve had this car for over three years and it has never run properly which is why I am pulling the head off over winter as the compression is low on number three cylinder. It is my aim to have a Somerset ready for next season that I dare to drive more than 20 miles away from home!

I will post the update once I have fitted another rebuilt pump.

Thanks again for your help and advice.

Kindest regards.

Robin

[charlie-farlie]

Hi again Dave.

Many thanks for your advice regarding the fuel pump. I followed your instructions to the letter and fitted the pump yesterday. I removed the top off the pump today and it was full. Before attempting to start the car, I dropped the bowl from the carb and it was empty, despite replacing the emulsion block and gasket. Therefore, I think that I must admit defeat and throw in the towel with this one! I will search for a good or new/old stock carburettor over the winter months while I have the head off.

Thank you so very much for all of your help and advice.

Warmest regards and best wishes.

Robin

[number5]

Hi there Robin,

The last time I stripped a similar carb was back in 1965, which was on a ’49 Hampshire, so my memory is a little faded.   Since 1967 though, I have had A90 Atlantics that have twin SU’s.  However, I do  have  ’54 Hereford engine on a test rig that I use for checking A70/90 gearboxes after reassembling them for testing. This engine only has around 35,000 miles on it, and the carby is original, which I think would be the same, and possibly pretty much like that on the Sommerset.  This engine can sit for many months in between starts, and when needed, apply the choke, and in a few seconds it is away.

From memory, in the base of Hampshire carby there is a small ball valve, and if the carb has been stripped for cleaning, and it is also supposed to have the ball valve, is it in place.  May I suggest to get an appropriate container ready with a block in its center, then to run your engine for several minutes, then switch off, and immediately remove the carb with the bowl full, sitting it on the block in the container.  Such should allow you to see if there is a leaking problem.

I have a fellow Atlantic owner, who in his younger days owned around 15~20 A40’s, though not sure if it included any Somersets. I have phoned him for some thoughts on your problem, but he has not thus far responded. I will let you know if he can offer anything that might be a cause of your problem.  I do think though that the check I have described should at least give some indication of a leak.

Hope it assists in some small way.

Happy Austineering,

Peter Hackney.

[charlie-farlie]

Hi Peter.

Many thanks for your message.

The ball valve is a little screws into the bowl beside the slow running jet. When it is removed, you can hear it moving if you shake it, so it is still in place.

I have had this problem and other bad running problems with my Somerset since we bought it in July 2018 and I am just about at the end of my tether with it. I have tried different carbs, different fuel pumps, renewed the fuel lines and swapped the fill her cap but have never been able to cure the problem.

A chap who I met at a show has a Somerset as a daily driver. He told me that he purchased a brand new Zenith carb for his car and it STILL ran badly. He cured his bad running by fitting an SU carburettor and electric fuel pump. I am seriously considering going down this route as I have tried just about everything else. Thankfully my car has got a good battery which considering how long it winds over before it starts, is a good thing! Failing that, I will open up the bonnet every day and prime the pump to fill the bowl. When I remove the head over the winter, I will strip the carb down and put it in my ultrasonic tank. (I have a fluid in the tank that I use when I overhaul clock movements). Then I will completely rebuild it myself instead of sending it to an expert again.

Thanks very much for getting in touch.

Kindest regards.

Robin

[charlie-farlie]

Hi Dave.

Many thanks for your reply.

I am aware of the differences between the two models and the carburettor used on each. The ball valve on my Zenith carb is in a tube next to the slow running jet, which is present and correct.

If I leave to car standing after a run or when leaving a show, it usually starts straight away, albeit sometimes needing a little choke.

I have done a compression test and number three cylinder is around 20lb lower than 1,2 and 4. This is why, on the advice of Graham Potts, that I am removing the head over the winter to perform a decoke. If I do a couple of runs totalling around 30 miles, or I start it and just move it three or four times, number three plug soots up. It is not wet and not only, just jet black with the other three plugs remaining in perfect condition.

The engine does not use any oil (it drips a little) and it doesn’t use any water at all. It doesn’t smoke, rattle or knock and the oil pressure goes straight up to around 50psi on start up from cold, dropping to 30psi when running hot. In fact, the oil pressure is normally up before the engine starts. I have checked and double checked the tappets. The plugs are gapped at 18. It has had a lumpy tick over since I got it, regardless of what carb I had fitted.

I will do as you suggest tomorrow as a final act and report back but I have tried three different carbs and this fault has been present on each one.

If I cannot cure this problem at all after doing everything I need to do over the winter months, this problem may well become somebody else’s problem, because I am at the end of my tether with it. I have managed to solve the mountain of other problems this car has had but even after the first 35 years of my working life spent in the motor trade, I have never had a problem like this that I cannot solve!!

Finally Dave, please see pages 18/ 19 of the new Practical Classics magazine and the picture of the club stand at the NEC!

Thank you again Dave for taking the trouble with this problem.

Kindest regards.

Robin

[charlie-farlie]

Hi again Dave,

Just to let you know that I dropped the bowl from the carb, popped in a tin, filled it with fuel and left it. After four hours, the base of the tin was barely moist. However, the outside of the bowl was very wet all round, suggesting to me that the bowl is either porous or has a fine hairline crack. The area around the emulsion block was dry. I decided to try the other three bowls that I have. One has a tiny hole in the bottom, one has a small crack around the emulsion block and the other seems to be fuel tight. I need to put this bowl in my ultrasonic tank and change the jets, non return valve, slow running jet and ball valve for the correct parts. This bowl is jetted for a Vauxhall Wyvern which also uses a Zenith 30-VIG carb. I am hoping after three years, it may FINALLY cure this fault. Just the new king pins to fit, a decoke to perform and an MOT to obtain!

Thanks for your help advice and patience with my fuel issues.

Warmest regards.

Robin

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