My 1932 BSA W32-6 500cc side valve will not start when the engine is hot. It will start when cold with just one kick and run beautifully, however if I stop the engine and attempt to restart it when it is hot it will not start.

I had this problem in 2017, which I solve by having the magneto rebuilt. I’ve done approximately 800 miles since the magneto was rebuilt by Tony Cooper (I believe he is now retired).

Could the magneto have failed again with such little use or should I look for other issues. I would be grateful to hear your kind advice and details about how to diagnose this and correct issue.

Yes, it sounds like a magneto problem. I have no idea who Tony Copper is but there are a lot of "professional" magneto re-builders who don't know what they are doing.

It is common for the wrong type of condenser to be used and they don't last long. And I have seen many re-wound wrong which causes the secondary windings to have an open circuit and make hot starting impossible.

Get the bike hot so it won't start on the top of a big hill so you can coast down and get some speed, then put the bike in gear. Does it start? If it does my first guess, is the condenser.

And another possibility, make sure the carb is not getting too hot. This will cause the fuel to boil and the bike won't start until the carb cools down.

Tony Cooper is still going though in his 70s now...Generally his work is good and trouble free...He did one for me recently...Ian

Tony Cooper is pretty much a reference amongst U.K. magneto and dynamo rebuilders. I believe he is ex-Lucas and has the full service agent test equipment etc. He's probably built more over many years than anyone else.

If there is a problem, I'd be pretty sure that it doesn't relate to incorrect procedure or skimping on components.

I have no connection to him, but there are so many examples of his work in use.

Tony has been trying to retire from repairing magnetos for some time now but still continues to supply proper parts to other magneto restorers. I'm sure he would be happy to test a magneto that he's recently overhauled.

Ron

email (option): ronpier@talk21.com

The last time I was up that way I visited his workshop one evening...Shelves and shelves of mags from all periods, newly manufactured adv/rtd units and points assemblies etc. etc...He's a man who enjoys his work and doesn't seem able to stop...(nice collection of bikes as well)....Ian

Yes, Tony is the best! worked for him in the 80's, those were the days buying brit bike stuff! His (then) brother in law worked at Lucas at the time, and so that's why he could have lots of stuff made.

Ian did you see the armature bearing install and removal machine?? something I was incredibly jealous off!!

Cheers,

Lex

email (option): welbike@outlook.com

Thank you everyone for your kind advice I will try Bruce’s condenser test then go and see Tony Cooper.

Based on your diagnostic advice I went on a long ride. The air temperature was 26°C, 69% humidity (hot and sticky). The bike started easily on the second kick, then ran beautifully.

I then stopped the bike at the top of the hill an immediately attempted to restart the bike, however it simply would not start, not even any signs of firing. So I tickled the carburettor until fuel was seeping out of the bottom wholes, then kicked it over but it still refused to fire. So I put the bike in second gear rolled it downhill until it picked up speed then let the clutch out, it started and rode all the way home without any hesitation.

When I got home I stopped the engine and immediately attempted to restart the engine, but again it would not fire up. I then sprayed some Holts Easy Start in the carburettor at which point it started and ran without any problem.

About 3 years ago I started to have issues when running the bike at temperatures over 20°C. After just under 2 miles the engine would stutter and come to a halt. The carburettor would be very hot, hence the petrol had become so hot it vapour locked the carburettor. I was using E10 fuel (in the UK this means it can have up to 10% Ethanol). I resolved this by using E5 in a see through container then removing the Ethanol by employing the water method (Ethanol is hydrophilic), after 2 days I remove the water, leaving just fuel. I also added a 6mm Tufnol spacer. Finally, I changed the route of the copper fuel line from the fuel tank to the carburettor from behind the cylinder head to the right-hand side, where it could be in the air stream.

Because the bike started when rolled down hill I thought that this pointed to the condenser, however because the bike will start on Easy Start, I’m not sure. What are your thoughts?

Check the spark with the engine cold...Then check it again when at running temperature....In both cases you should have a good, strong, blue spark..If you have a weak white spark when hot that may well be the mag...Gap the plug to .018" if you haven't already...What plug are you using? (Make and grade)....Ian

Thank you Ian for your advice. My spark plug is a KLG Super M30. I will try the things you suggest tomorrow.

My first guess was the condenser as you described the symptoms of it failing. But there are other causes and am now guessing the carb is getting too hot. Usually if the condenser is failing, the bike will start going down the hill but wont run very well but will get you back home.

My M21 on a hot day when stopped, will in a about a minute start boiling the fuel in the float bowl. It will not start until it cools down or you tickle it long enough to get cooler fuel into the float bowl. Riding the bike, the air flow keeps the carb cooled. The problem does not happen in the winter. Where I live it can on occasion get to 46 degrees C (115 degrees F) in the summer. My M20 and M21 both will run OK in this temp as long as you keep moving. These are temperatures that probably no one in the UK has ever seen.

I once measured the cylinder head temp at 575 degrees F.

Ian's saying to check the spark at the plug, is a good idea.

And another way to check the condenser is to run the bike in the dark and look at the points. They should have a very small spark when they open. If the spark at the points get a lot bigger when hot, you probably have a bad condenser.

As I can't see the bike, I can only guess as to what the problem is from 48 years of riding M20's. So I now think your carb is getting too hot?

And to add to this, if your ignition timing is retarded? this will also add to the engine running hotter. My experience with failing Champion and NGK plugs has led me to use Bosch W8AC in my SV's and W7AC in my OHV's. Ron

email (option): ronpier@talk21.com

I don't recognise the "Super" classification, but the KLG M30 is a very hot plug, intended more for cars with an oiling problem. A hot air-cooled sidevalve would usually have at least an M50, probably an M60...Nortons use an M80.

Hi Jon
Running original old plugs does work for some people but in my experience if you want to get somewhere you run a modern plug. and randomly picking one of the wrong temperature isn't going to help.

Buy a new Bosch like Ron suggested and then see if you have a problem to resolve.

Rob

email (option): robmiller11(a)yahoo.co.uk

I did my usual 41 point maintenance schedule on 10/05/2025, which I do every year when I get the bike out of it’s hibernation. I also have a winterisation check list which I do in October each year, which includes things like removing the fuel from the tank and carburettor.

The bike starts on the first or second kick and runs beautifully, however if I stop the engine after riding the bike at 25°C or above I can only immediately restart the bike by using Easy Start or running it down hill, which will eventually draw fuel through the carburettor.

I’m beginning to suspect that the spark and hence the Magneto may not be the cause of the problem, because once the bike is restarted it will run without any problems. I think the facts are pointing to the fuel boiling off as soon as I stop, requiring me to restart by either using Easy Start, running the bike down hill or simply giving it enough time to cool down.

Are my expectations of a 92 year old side valve motorcycle running on modern fuel unrealistic? Should I just live with the fact that restarting my hot bike in hot weather will require a little rethinking (hence the problem is with me) or should I continue to explore more ways of getting the bike to run cooler?

I’ve based my maintenance schedule on BSA guidelines for a W32-6 500cc side valve motorcycle, written in the 1930s, which means they are based on 1930s fuel.

1, Contact breaker point gap when the piston is at TDC, is 0.003 inch with the lever set at fully retard. This has been set in accordance with be information given by BSA for this bike.
2, Tappet clearance Inlet = 0.004 inch, Exhaust = 0.006 inch. Again this has been set in accordance with be information given by BSA for this bike.

I’m open to your thoughts about the points gap being set to 0.003 inch at TDC, given that the main variable change in this case is modern fuel.

I will also do some investigation into which modern Bosch spark plug will fit my motorcycle, thank you, for your kind suggestions about spark plugs.

Setting the points gap at TDC fully retarded makes no sense? How do you even know if the magneto is even close to being timed correctly at TDC? You could be 90 degrees off and the points not even open at TDC to check for a .003" gap? So if you just put the magdyno back on the bike, how do you set the gap with the timing way off?

What is the points gap when they are fully open? I have never heard of setting the gap at TDC but always turning the motor until the points are open all the way.

A M20 you set the gap at .012" with the points open all the way. You don't care about TDC except for timing the mag.

Now granted I have never seen a BSA W32 and don't even know what model Lucas magdyno it has.

I have a 1929 AJS so close in year to your bike and the points gap on it's Lucas magneto is supposed to be set to .019" fully open. TDC means nothing for setting this. I also have a 1936 Triumph and its gap is set to .012" fully open. Again TDC means nothing for setting the gap.

Does he mean with the points gap set at 12 thou as usual. Set the timing at TDC on full retard (points breaking at 3 thou) instead of 7/16" BTDC on full advance (points just breaking). I have heard other guys who say they set there timing at TDC retarded. Likewise I have no idea about this pre war instruction. All my bikes are timed at Full advance BTDC. Ron

email (option): ronpier@talk21.com

Interestingly my M20 has been getting easier to start.
Fully advanced, no trouble.
Now it's done just shy of 2000 miles I thought I really should check the timing.
As the fuel tank was off to reroute some cables, I thought I'd time it with the head off.
It seems that the timing has slipped! It was more like 1/4" before TDC fully advanced.
Points seem to have opened to 0.014" and the tappets closed to 0.008" and 0.010"
It might have a little more performance now.
The point I'm making is that it's worthwhile checking settings once in a while.

Mark

email (option): pes.sales@btconnect.com

Could you please have a look at the below images and give me some feedback on what the condition of the spark plug and exhaust valve (on the right) are telling me about the running condition of the bike.

Thank you for your kind advice my BSA is now running better than it ever has.