1
British Bikes / Re: Hot Start Problem
« on: July 24, 2025, 09:20:41 PM »
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.
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2
British Bikes / Re: Hot Start Problem
« on: July 07, 2025, 10:44:19 PM »
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.
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.
3
British Bikes / Re: Hot Start Problem
« on: July 03, 2025, 09:51:36 PM »
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.
I will let you know how I get on.
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.
I will let you know how I get on.
4
British Bikes / Re: Hot Start Problem
« on: July 01, 2025, 10:12:40 PM »
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.
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.
5
British Bikes / Re: Hot Start Problem
« on: June 30, 2025, 09:42:19 PM »
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 for cold engine.
Click HERE https://www.youtube.com/watch?v=9qWQgNpN07Q for hot engine.
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 for cold engine.
Click HERE https://www.youtube.com/watch?v=9qWQgNpN07Q for hot engine.
6
British Bikes / Re: Hot Start Problem
« on: June 29, 2025, 08:34:42 PM »
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?
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?
7
British Bikes / Re: Hot Start Problem
« on: June 29, 2025, 06:52:33 PM »
Thank you everyone for your kind advice I will try your ideas.
8
British Bikes / Hot Start Problem
« on: June 28, 2025, 10:17:40 PM »
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.
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.
9
British Bikes / Re: She's hot
« on: June 03, 2022, 10:32:00 PM »
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.
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.
10
British Bikes / Re: She's hot
« on: June 01, 2022, 02:00:25 PM »
Hi Ian,
Not being able to see the images is an issue at your end, other can see them. Try updating your web browser, or using a different web browser.
Not being able to see the images is an issue at your end, other can see them. Try updating your web browser, or using a different web browser.
11
British Bikes / Re: She's hot
« on: May 31, 2022, 06:49:52 PM »
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.
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.
12
British Bikes / Re: She's hot
« on: May 31, 2022, 12:35:02 PM »
Yesterday, I tightened the cylinder head bolts to 30 foot pounds, then set the engine at TDC using a gauge I made from a wire coat hanger. After this I set the contact breaker points gap to 0.003 with the ignition fully retarded, these are the instruction in the BSA book for my model.
Today I went for a half mile ride; I stopped early because it had started to rain hard; however I could see smoke coming from the cylinder head again. Hence the next thing I intend is remove the cylinder head anneal the copper gasket and use Wellseal to improve the seal.
I will take photos of the head and post them.
Thanks again for your advice.
Today I went for a half mile ride; I stopped early because it had started to rain hard; however I could see smoke coming from the cylinder head again. Hence the next thing I intend is remove the cylinder head anneal the copper gasket and use Wellseal to improve the seal.
I will take photos of the head and post them.
Thanks again for your advice.
13
British Bikes / Re: She's hot
« on: May 29, 2022, 04:45:58 PM »
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.
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.
14
British Bikes / Re: She's hot
« on: May 29, 2022, 08:45:10 AM »
I’m a little embarrassed to tell you this, however the reason why the ignition lever would always return to retarded was because the nut had worked lose, after tightening the nut I can run on constant full advance. I had previously identified that this nut would work lose so had put some lock wire around it to stop it turning, however over time the lock wire around the nut was insufficient. When I first realised this I thought that I had finally found the solution, but I’m afraid I’ve only found part of the puzzle, because after riding four miles on full advance at 17 C (air temperature) the bike was so hot that smoke was coming from the cylinder head. So it’s not the ignition timing.
Should I take the cylinder head off an look for heavy carbon deposits, could it be that I need to decarbonise my bike, would that make it run so hot?
Should I take the cylinder head off an look for heavy carbon deposits, could it be that I need to decarbonise my bike, would that make it run so hot?
15
British Bikes / Re: She's hot
« on: May 26, 2022, 11:15:24 PM »
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.