classic motorcycle forum
Motorcycle Discussions => British Bikes => Topic started by: Billington on June 28, 2025, 10:17:40 PM
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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.
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Sounds like a failing condensor again, doesn't it. !
Do you know what the rebuild used - not a NOS one, we hope. ?
Another possibility is vapour lock.
Have you checked to see how warm the carb/manifold is when you pull up.
Those heat insulating tufnol type gaskets were added to many a model,
to help prevent this happening in hot weather.
So if you pour icy water over the carb and it still won't start, then try it over the maggie.
Preventing water ingressing to inside the works - a tricky situation.
Have fun, tell us how it goes ...
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Of course the magneto could fail after little use. Age and how it has been stored since last done can have serious consequences regardless of mileage done.
I’m currently amusing myself with three radio controlled helicopters. All N.O.S, all received in their original unopened packaging, all looking perfect but all non running due to battery failure through sitting around for the last ten years or so. Electrical equipment can do that if left sitting. Look good externally but moulder away internally. Very frustrating but that’s how it is.
As R says it could also be vapour lock. Side valve engines do tend to run hotter than their OHV equivalent and I have seen some poorly thought out fuel line arrangements as well as R’s failure to fit a Tufnol heat barrier twixt carb and cylinder.
Nevertheless I tend towards electrical failure as my own experiences with vapour lock have been on stinking hot summer days with the engine smelling like a fifty year old fish and chip shop on a busy Friday night. Not just a mere hot start issue.
Tell us how you get on.
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Fail to start can also be flooding of a hot motor ...........I diagnose start problems with a can of starting spray ......this stuff will fire with flooding or with fuel starvation .......but it wont fire with no spark.
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Thank you everyone for your kind advice I will try your ideas.
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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?
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Did you feel the carby and manifold - was it warm/hot. ?
Sure sounds like fuel, doesn't it.
Have you drained the carby floatbowl, and inspected what comes out.
I had a rash of rust particles and little water droplets.
Must have bought some dirty fuel someplace
(fuel by law is allowed to contain up to 2% water !!).
Sure didn't like burning that stuff ...
P.S. Tried a new spark plug ?
They don't last forever...
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Thing is, if it was shite in the float bowl it would cause problems whether hot or cold..
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Thank you R and Rex, I drain the carburettor and fuel tank once a year so I think there is no issue with rubbish in the fuel. I would welcome some more advice on weak sparks and vapour lock.
I have produced two videos of me kicking the bike over with the spark plug out of the cylinder. The first video is when the engine is cold and the second is when the engine is hot. Rather than being blue the spark looks white.
I’m using a KLG M30 spark plug; I mistakenly said “M20” in the video.
Click HERE https://www.youtube.com/watch?v=3qxDJLp57u8 (https://www.youtube.com/watch?v=3qxDJLp57u8) for cold engine.
Click HERE https://www.youtube.com/watch?v=9qWQgNpN07Q (https://www.youtube.com/watch?v=9qWQgNpN07Q) for hot engine.
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Thing is, if it was shite in the float bowl it would cause problems whether hot or cold..
While this is quite true, I have found that cold engines are very sensitive to this,
and once warmed up they will start near regardless.
Even if they then run like a dog - but this instantly tells you something is up.
Could the easy start spray to make it start be because of a weak spark ?
I have enough old iron that I keep a spare magdyno on the shelf.
This ensures they never play up !
The 1932 version may be a bit pricey for this, and it can be a lot of work to swap over.
But worth considering if this persists ?
Someone here had persistent starting problems, and borrowed such a spare maggie to try.
It proved equally difficult, but in the course of this the earthing path was improved.
Instant success ! Think laterally ?
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I’ve been thinking of other possibilities. My vintage side valve experience mainly comes from operating a 1926 Matchless. This has a splash and hope total loss lubrication system with exposed valves and sloppy provision for valve guide lubrication. This created some entertaining stoppage issues that took some time to diagnose and even longer to effectively resolve. As your BSA is only a little younger I was wondering whether you might have the same.
The one that most closely resembles your problem was a sticky exhaust valve. This was over lubricated as the piston did not have provision for an oil control ring (pointless with a total loss lubrication system) much oil disappeared down the exhaust pipe clagging up the exhaust valve guide on the way. This caused mysterious stoppages and refusal to start for no apparent reason. Any sort of fiddling with the engine, checking fuel, checking spark, etc, allowed the engine to cool down, the valve freed itself and it would happily restart with me thinking it was my successful fiddling that did the trick, not the cooling off.
I’m not saying that is your problem precisely but I am saying your problem may lie in the valve operation. Guides slightly too tight, valve lifter a fraction tight and so on. It doesn’t take much for valves to not quite seat when hot yet be fine when cooler.
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Hopefully you have set the points gap to 12 thou and set the magneto timing correctly. https://classicmotorcycleforum.com/index.php?topic=6299.msg31348#msg31348
If you haven't, do it now.
Leon
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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.
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Is there any time in the rotation of the magneto that the points open to 0.012"? I assume no.
Do your bike a favour and get someone who knows what they're doing to have a look at it. You will be amazed at how a 92-year-old side valve runs when it is properly set up.
Leon
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Ah, we're back to this case are we ???
Yes, if the ignition timing is so off that the engine is on the point of meltdown,
then all bets are off.
Get the ignition set correctly, as suggested ....
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Jon, you are discussing this problem with a group of Australians all of whom regard 25degreesC as merely balmy, not hot at all and who play with vintage and veteran machinery much older than yours. As a 1932 model pedantically your bike isn’t even vintage. You may have a hot start problem but warm weather and age of machinery are not the root cause of your woes. It lies elsewhere.
I have a practical guide to BSA from 1931 written by D W Munro of BSA and first published in 1948 by Pearson in front of me. In his chapter on servicing old models Mr Munro goes on at length about “The Importance of Correct Ignition Timing” for nigh on two pages, finishing off the second page with other possible causes being weak mixture, tight valve guides, burnt valves and insufficient exhaust tapped clearance.
It may be time to again look closely at all these matters.
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Yep, always best to go "back to first principles" and check everything, especially when you see some of the dumbarse instant solutions on the Net.
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I’ve been plodding through my early BSA literature. It’s made interesting reading. I hadn’t known BSA gave their ignition timings using full retard for several years. They came in line with standard practice sometime in the mid-30’s. They did a full turn around ferociously emphasising all magneto ignition timings were on full advance. In 1936, the last year of Mr Billingtons particular BSA ignition timing was now listed as 7/16” at full advance.
It was a similar curious story with the tappet settings. They were steadily increased over the life of that particular engine. Mr Billington is correct in saying the settings were inlet .004” and exhaust .006” in 1932 but had listed them as .004 for both the year before in 1931 and increased the exhaust setting to .008 for 1933-36.
Lots of food for thought there isn’t there.
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That is interesting.
In particular the 0.004/0.004" valve clearances in 1931 seem very optimistic, very precise. I must admit that I don't use a feeler gauge at all on my vintage bikes, but just give them a jiggle to make sure they're ok. I reckon 4 thou on an exhaust valve wouldn't pass my jiggle test!
As for setting ignition timing using engine at TDC and mag on full retard, I do it all the time - it's my standard method on the side of the road. Easy to find TDC, easy to spot the points starting to open (in the BSA case open 3 thou - a quarter of the way to 12 thou). Done. Works every time. But, depending what has been done to the mag over the years, it sometimes means too much advance is available to the engine with the lever at full advance, so maybe the bike runs best on no-quite-full advance. Over-advanced ignition is bad. Not a problem for an experienced rider, but bad in the hands of a novice. Best to set the timing at full advance if you're at home in the shed.
Seriously, I wish Billington all the best with his bike, but he seems to misunderstand the BSA instructions yet stands by his misunderstanding even when others try to explain. I have done my best.
Cheers,
Leon
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Thank you 33d3 and Rex, I have a copy of Munro’s “BSA a practical guide covering all models from 1931”, which I have read and applied it’s settings to my bike. Your point about tappet clearance is interesting; page 189 shows how the exhaust setting changed from 6 to 8 thousandths of an inch from 1932 to 1933 for essentially the same engine. It’s tempting to rationalise that this increase may have been to reduce engine temperature by creating a bigger passage for hot gases.
I would like to make a reference from page 82 of the same book. Below is an excerpt for those who do not own a copy of the book.
Ignition
No improvement can be expected from an alteration to the ignition timing. In fact the reverse is almost invariably the case, too much advance producing roughness, without any speed increase, while a retarded spark causes sluggishness and overheating, although the owner may be tempted to retard his ignition a trifle in order to take advantage of the slightly greater flexibility thus obtained. Yet it is a certain fact that many owners re-time their engines as a matter of course as soon as the dealer’s back is turned. This is proved by the number of machines which find their way back to factory repair departments, or to repairer’ premises, with ignition timing hopelessly out. And it is significant that the complaints for which such machines are returned is often attributable soley to the experiment on the owner’s part.
I do not reference this passage for churlish point scoring reasons, merely to clarify my reasoning for not making changes that are not evidence based. It is with an orderly mind and a logical neatness that mechanics diagnose and resolve issues. Hence I will make a test table, which is my usual practice that records incremental changes made, the rationale for making the change and the outcome. This has ensured satisfactory conclusions for technical problems for me in the past.
I will include the following tests and changes, individually, within my causes of overheating test table
1, Weak fuel mixture
2, Burnt valves
3, Carbon build up
4, Insufficient exhaust tappet clearance
6, Increase exhaust tappet clearance
Finally, yes, I will be using Magneto setting contained within the “BSA Motorcycle Instruction Book”, but rather than use the “All models 1930 to 1936” I will use the “1932 Models” edition. The reason for this is that it has a clear diagram showing a Lucas Magneto with the follower about half on the start of the cam.
This image shows where I set the points to 3 thousands of an inch, which I now believe could be about 40° to late. I was informed to use this point by someone with significant knowledge of Magnetos, but I think he expected me to use this when the piston was at 3/8 before TDC.
(https://classicmotorcycleforum.com/index.php?action=dlattach;topic=6299.0;attach=7993;image)
I will let you know how I get on.
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It is not entirely clear (to me) what method you are now going to use to set the ignition timing,
but I'd comment that if it is not going to verify that it is sparking at that 3/8" BTDC at full advance,
then we might be back to square one ?
And, the fuzzy logic of "hot gases" escapes me also. If BSA increased the tappet clearance, it is
very likely that they found the valve was growing with heat, until it lost any clearance.
At this point it may/would/could start losing compression - which may make them
a) difficult to restart
b) begin to burn a valve, since the hot gases would/could be continuously escaping.
And this would not be good.
Hopethishelps
Have fun !
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Hi Billington,
In your photo the rubbing block is well past the opening ramp: when it is in this position the points gap should be about 0.012".
For most of the rotation of the magneto the points should be open about 12 thou; for the rest the points should be closed. Only when the rubbing block hits the ramps and begins opening the points will the gap pass (instantaneously) through 0.003". (And again when closing, but this plays no role in the spark.)
When BSA talks about the points being open 0.003", they mean that the rubbing block has hit the ramp and the points have opened about a quarter the way to fully open (0.012"). This defines an exact point in the rotation of the magneto.
You've asked for help, we've provided it with care an attention. Have you considered accepting it? Humour us. Try it out.
Cheers
Leon
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Oh, and by all means use the BSA method of points 0.003" open with the magneto on full retard and the engine at TDC. But you have to first set the points gap to 12 thou (no doubt listed somewhere in your BSA literature?), then set the timing by moving the magneto gears, not adjusting the points gap.
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No wonder the factory was getting back lotsa bikes with faulty running !
Sounds diabolical.
Just how do you "set the timing by moving the magneto gears" ??
Or is that the time honoured method of tapping the gearwheel onto the taper, and then locking it with the nut ...
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Just how do you "set the timing by moving the magneto gears" ??
Or is that the time honoured method of tapping the gearwheel onto the taper, and then locking it with the nut ...
Whatever... within half a tooth would be enormously better than it is now.
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The OP could do the "quick and dirty" test to see if the problem doesn't lie with the mag or timing, namely set to TDC on comp stroke with lever fully retarded, then move lever incrementally advanced to find the best position and so prove the rest of the engine, carb etc.
If nowhere within that lever range produces a good running engine then you need to look elsewhere.
At full advance of the hand lever the timing will likely be too advanced so will need resetting at some point.
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Probably best to be sure the magneto advance diection is still the same direction the maker intended ......I can tell by the change in exhaust note if ignition advance is right.............the army bike instructors used to do a trick of flooding the M20 carby and kicking the bike on full advance .......the carby would catch fire and they would pretend not to notice ........then when the fire was getting a bit big,retard the mag ,kick the bike and suck all the flame into the carb.......they reckoned that the motor would always start with the carby on fire.
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I just put the bike on the lift and tried the old cigarette paper trick. It was not possible to remove the cigarette paper from between the points until the rubbing block was about 30° past the opening ramp! I did not set it like this, but I will correct this.
Strangely the bike does run okay like this, it simply has issues with hot starting.
Thank you again to those who have offer kind advice.
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Good that you found it.
Must have been getting somewhat hot and bothered inside - hence the reluctance to start again.
The final proof will be in the fixing ....
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A pre 36 maggdyno will have a ring cam ,and quite often these rings are very worn,altering the timing adversely..........you cant regrind the ring ,as its case hardened ,and once the hardening is worn thru ,very soft steel.
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Usually you'd just reset the timing to suit. ?
Banging the gear onto its taper, and ensure it doesn't shift while doing so, etc.
If the gear shifts on its taper, maybe it needs to be ground in, to get a better grip ?
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Thank you for your kind advice my BSA is now running better than it ever has. Advancing the magneto timing a little has ensured that it’s now in the sweet spot.