classic motorcycle forum

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 been servicing my 1932 BSA, which has a cam ring contact breaker. In one of the BSA books I own the indicated gap size is .003” when the piston is at TDC, with the ignition is fully retarded. When I measured the gap it was .006”. So I was thinking about adjusting the gap until I read in “Book of BSA” (Year and model appropriate), “with the contacts full open, should be considerably more or less than will just hold a 12 thou’ blade of a feeler gauge(0.012 in.) they should be adjusted. ”

The bike seems to run just fine and the spark plug is a light brown colour. So should I adjust the gap to .003” or just leave it alone?

I’ve noticed that some people working on 1950/60s British motorcycle sometimes change fibre washer to Dowty washers to prevent leakage. Is it advisable to use this types of washer on a 1930s bike. Also when would you advise using a Dowty washer over a standard fibre washer.
Thank you for any advice.

It’s hot (28 C) and my 1932 BSA doesn’t like it. The bike experienced vapour lock after traveling just 1.5 miles, hence I’m going to try a Tufnol spacer to reduce heat transfer to the Carburettor body.



Will the spacer act like a gasket or should I place a gasket either side of the spacer?



Thank you for any help.

My W32-6 1932 BSA 500 cc side valve starts and runs fine now I’ve adjusted the Throttle Stop and Pilot Air Screw so that it will tick over slowly when the throttle is closed. However when on a long run the other day I came to a long downhill section, I closed the throttle because I did not need to increase the speed, when I opened the throttle again at the bottom of the hill the engine simple didn’t pick up. The motor died and I pulled over to the side of the road. I had been riding for about 20 minutes in 20 C temperature.

By looking at the Primary Air Holes I could see that no fuel was present. I allowed the bike to cool down for a few minutes and pressed the Tickler on the Carburettor, fuel could be seen bubbling an evaporating through the Primary Air Holes. I waited another few minutes then pressed the Tickler on the Carburettor, fuel could now be seen following out of the Primary Air Holes as normal; hence I started the bike and road the 6 miles home without a problem; however I made sure that I didn’t allow the throttle to completely close to avoid a re-occurrence of this problem.
I think what may be happening is that the Carburettor is getting so hot that the fuel is evaporating before it enters the cylinder. Does this make sense and if so how can I prevent this from happening.

I need a new helmet, I’ve had my LS2 FF370 for over 5 years.

Should I go to a shop or buy online?

Where is the best place to buy online?

I hope you can help me, my 1932 BSA W32-6 (500cc side valve) is losing power when I change up to third or fourth gear, but only when riding on the flat.

The bike is not easy to start but when it does start it pulls away just fine in first gear then pulling strong in second. However when I change to third or four gear the engine revs drop and the bike would stop if it did not change down to second again.

I find this strange but what I find even stranger is that the bike works fine when either going up or down hill in third gear.

What is causing this and how can I solve it?

Thank you for any helpful advice.

My bike will not start. Please read all my post before responding

After having difficulty starting my BSA W32-6 4.99 hp side valve (1932) when it was hot I had the magneto professionally rebuilt. I was also advised by Tony Cooper who rebuilt the magneto that it would be more reliable to replace the original Lucas three brush dynamo with a later Lucas two brush dynamo; so I did. Hence I have a Lucas MS1 magdyno fitted, with a later Lucas dynamo.

Tony also advised me to replace the mechanical regulator, which was a coil on the back of the control panel switch (Control switch setting are off, charge, High beam and low beam). He told me it would be better if I replaced it with a Teb-tec solid state encapsulated regulator. Again I have done this.

When I replaced the magdyno I removed the cylinder head so that I could see that it was at Top Dead Centre, when the piston was at the top and both inlet and outlet valves where closed. I then located the magdyno into the sprocket with the ignition in fully retarded position. This is the method stated in the BSA Motor Cycle Instruction Book (All models 1930 to 1936 inclusive). The exact wording for all 1932 BSA motorcycle is:

Piston at T.D.C Ignition fully retarded, Contact Breaker points open .003”

Before locating the magdyno into the sprocket I had rotated the contact breaker assembly until a cigarette paper could just move between the points and left it where the cigarette paper just comes loose. I made sure that it was fully retarded by not connecting the cable to the leaver, hence the cable was loose.

Both the inlet and outlet valve (Tappet) clearances are correct, .004” inlet and .006” exhaust.

When I attempt to start the motorcycle it will not fire at all. I tired starting the bike fully advance, half advance and fully retarded; however the outcome was always the same it would not fire at all. So I did the usual check for air fuel mixture and spark at the spark plug. I removed the spark plug placed it against the engine and yes there was a spark, also fuel was gently dripping out of the carburettor which indicates that the fuel was getting through.

Then I tried spraying Easy Start down the carburetter mixing chamber, again I tried bike fully advance, half advance and fully retarded. It would only back fire sending the force back through the kick start.

My question is how do I diagnose and remedy this problem.

Thank you for your kind help.