Forums General Counties Cars Discussion A40 Somerset fuel drain back. Reply To: A40 Somerset fuel drain back.


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.