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Leon, thank you so much for your detailed response, I really appreciate your time and effort to share your expertise on old bikes. I’ve printed off your response and placed it in my BSA ring binder.

Before reading your response I completed my top end overhaul, which included torqueing the head bolts several times, when cold and after running the bike to get it warm. The bike now seems to be air tight at the cylinder head. On my 3 mile ride today it is now pulling strongly up the hills where I live, however this was not long enough for me to satisfy myself that I’ve completely resolved this issue. If the problem of overheating continues to happen I will follow the steps you have outlined.

There are other issues I’ve been working on with the advice from you and others such as how to ensure the ignition lever has enough friction to stop where I’ve put it, currently I ride the bike with one finger rapped around the ignition lever, which results in hand cramp after 10 minutes. Also getting it to idle just right, but these are all problems I will persevere with overtime.

Thank you again for any ideas and advice you may have given.

The pictures with this post are as a result of me taking the cylinder head off today, because it was leaking smoke which was not solved by tightening the head bolts. Also the bike is running hot possibly due to the air fuel mixture being lean due to the air being drawn in past the cylinder head gasket.

Pictures

1, The spark plug with a light brown indicating hot or lean
2, Contact breaker when the piston is at TDC. The point gap is 0.003 in this picture. This has been set in accordance with be information given by BSA for this bike.
3, Copper head gasket before cleaning. You can see the black marks at the top and bottom of the gasket where smoke was coming out.
4, The Copper head gasket after being cleaned with a Brillo pad, scotch brite and annealed.
5, Cylinder head before cleaning. You can see the shiny marks where smoke was escaping.
6, Cylinder head after cleaning.
7, Piston and valves before cleaning. Again you can see the shiny marks where smoke was escaping.
8, Piston and valves after being cleaned with a Brillo pad, scotch brite.

My thinking has moved on to the point people have been making  about weak fuel mixture and leaks at the head gasket. I had checked and tighten the cylinder head bolt as part of my spring service notes after taking the bike off the road in the autumn, but I now realised that I had set my torque wrench to 30 newton meters, but my notes state 30 foot pounds, which would equate to 40 newton meters.

When I stopped the bike yesterday smoke was coming out of the head gasket, which would indicate that is not hermetically sealed, there was also a shiny oil mark on the cooling fins that come from the cylinder head. All this would point to the cylinder head not being completely airtight. If smoke can get out air can get in during the intake stroke.

I will set the cylinder head bolts to their correct torque setting and see if this makes a difference. If it does not I will remove the cylinder head anneal the copper gasket again and refit the cylinder head.

Part of the problem is that the ignition advance/retard lever does not stop in position I have turned it to. It slowly returns to closed which equates to full retarded. The friction available on the lever does not seem able to overcome the spring in the magneto.

I went for a ride today to try the ideas suggested in this link (air temperature 10 C). My first ride I tried the air lever full open and the ignition half advance, however the results were poor, the bike did not get so hot that it vapour locked but is ran poorly an cut out on the one mile run.
In the afternoon I changed the oil and played with the throttle stop; I could set it a tick over but if I stopped the bike and started it again it would then stall on closed throttle which seems inconsistent. However I went for a 3 mile ride (air temperature now 17 C), with the air lever closed (because I had forgot to open it!) and trying different ignition positions as the road dictated (I live in a very hilly area of England). The bike did not stall because I was managing this with the throttle. At the end I could touch the carburettor but it was still warm.
Thank you for all your advice and questions.

Hi Leon, thank you so much for the advice. You have given me a starting point for things to try. I will be working over the next two days, so on Wednesday I will try starting the bike by setting the throttle at about on eighth open and the air lever shut. Then move the ignition control to about half full advance. I will flood the carburettor by depressing the tickler for a short time only. As soon as start I will move the ignition control to fully advanced position, when the engine is warm I will open the air lever about three quarters of its travel. I will let you know how I get on after a test ride.
The carburettor details are as follows:
BSA W32-6 Carburettor
Type = Amal 6/112
No = 45A
Float Chamber 64/079
Jet =140 (Main Jet) B140)
Needle = 1
I set the Magneto timing by the BSA instruction book, however I’m not sure if these instruction work for both 1932 quality fuel and 2022 quality fuel.
I use regular petrol in my bike. If I’m honest I did not look at the E value when I purchased the petrol but I will have a look next time I’m filling up. I did however put about 25ml of Redex Lead replacement fuel additive. I’m not shore if this could have an effect.
To set the magneto timing I followed these BSA instruction.
Release the magneto pinion and set the piston at top dead centre of the compression stroke. The ignition is timed in the fully retarded position. With the piston at T.D.C and the ignition fully retarded I set the contact breaker points open .003 inch, then re-tighten the magneto pinion.
Thank you for any helpful contributions.

Today I took my 1932 BSA 500cc sv, out for the first time this year. After checking it over and adding fresh fuel it started on the second kick. I then went for a ride, after just under 2 miles the engine stuttered and can to a halt. The carburettor was very hot, hence the petrol had become so hot it vapour locked the carburettor. I let it cool down for 10 minutes and it started up again so I rode home.
I had is problem in 2019 when the air temperature was about 20 °C. The kind advice from this forum indicated that I needed to fit a Tufnol flange spacer, which I did. After fitting the 5mm spacer the bike ran okay in temperatures up to 28 °C. However the temperature today was only 16 °C.
I know what the problem is, its vapour lock. My question is why is it now happening at a lower temperature and is the only solution a thicker carburettor flange spacer?

I've now ordered two bulbs from two different places and will run some tests with a digital volt meter. I know the bulbs cloud over and stop working when the engine is not running.