I can only reach a top speed of around 55mph.
Bike only starts on fully advanced . If I retard bike even the slightest it will not start.
Bike starts 1st time and pulls very well.
I have timing set to 7/16 ( 37 degree) BTDC. ( timing set when filly advanced)
Everything has been checked.
If I set timing to 40-41 degree BTDC, will this increase my top spead?
Thanks in advance
Brian
No. It might put a hole in your piston. It sounds as if the valve icing is out by a tooth.
What are the symptoms when under power at full speed or up into your revs if you manually retard your timming? Just to rule out any confusion of the slack/tight wire posablilites of how your manual advance works?
Apologies if you're already aware of this Brian, but is your mag a slack or tight wire advance?
Starting on full advance would probably result in kickback through the kickstart are you sure the timing is set correctly.
If it will not start with any retard setting could mean your mag has a weak spark.
Quote from: WayneBergman on 18 Dec, 2023, 01:19
What are the symptoms when under power at full speed or up into your revs if you manually retard your timming? Just to rule out any confusion of the slack/tight wire posablilites of how your manual advance works?
Hi Cams checked and all ok.
Cheers
Brian
Quote from: WayneBergman on 18 Dec, 2023, 01:19
What are the symptoms when under power at full speed or up into your revs if you manually retard your timming? Just to rule out any confusion of the slack/tight wire posablilites of how your manual advance works?
hi
Bike is tight advance, no kick back when kicking over. When at highest speed bike runs fine and runs fine when getting to my top speed
Quote from: Ian C on 18 Dec, 2023, 09:01
Apologies if you're already aware of this Brian, but is your mag a slack or tight wire advance?
Bike is defintely tight wire advance.
Cheers
Brian
Quote from: JulianS on 18 Dec, 2023, 09:07
Starting on full advance would probably result in kickback through the kickstart are you sure the timing is set correctly.
If it will not start with any retard setting could mean your mag has a weak spark.
No kick back on full advance, which makes me think that I could advnace timing a little more?
When bike warmed up I can retard whilst sitting at traffic lights etc. , however not by much.
Bike always started well when I got bike but top speed was even lower ( 45mph) and would not pull me up a hill etc.
I checked timing and it was set at 47 degrees BTDC. Under furher investiagtion, it had wrong carb and the slide was very obviously badly tampered with.
I bought correct carb from AMAL which came preset and seems to be working fine. I also put new points in and spark plug.
Top speed now 55mph set at 37 degree BTDC. Bike always starts and seems to be a new mag.
Cheers
Brian
My B32 will only do 55 mph max in top gear despite the engine being in very good condition, the timing accurately set and the carburation good. I understood why a couple of months ago when I was looking at the specs for the various BSA pre-unit singles and realised that my bike has a 19 tooth engine sprocket fitted by a previous owner but should have a 17t. It has been pulling B33 gearing. No wonder it wouldn't go any faster. I have a new 17t ready to fit over the winter.
Quote from: Derek996 on 18 Dec, 2023, 14:16
My B32 will only do 55 mph max in top gear despite the engine being in very good condition, the timing accurately set and the carburation good. I understood why a couple of months ago when I was looking at the specs for the various BSA pre-unit singles and realised that my bike has a 19 tooth engine sprocket fitted by a previous owner but should have a 17t. It has been pulling B33 gearing. No wonder it wouldn't go any faster. I have a new 17t ready to fit over the winter.
My bike is a 1953 BSA B31 S, it also has a 19T engine sprocket but I'm nearly sure that is the correct one. The rear break hub sprocket is 42T
Cheers
Brian
Quote from: briancairns on 18 Dec, 2023, 14:29
Quote from: Derek996 on 18 Dec, 2023, 14:16
My B32 will only do 55 mph max in top gear despite the engine being in very good condition, the timing accurately set and the carburation good. I understood why a couple of months ago when I was looking at the specs for the various BSA pre-unit singles and realised that my bike has a 19 tooth engine sprocket fitted by a previous owner but should have a 17t. It has been pulling B33 gearing. No wonder it wouldn't go any faster. I have a new 17t ready to fit over the winter.
My bike is a 1953 BSA B31 S, it also has a 19T engine sprocket but I'm nearly sure that is the correct one. The rear break hub sprocket is 42T
Cheers
Apologies, engine sprocket is 17T and gear box sprocket is 19T
Brian
Quote from: briancairns on 18 Dec, 2023, 14:43
Quote from: briancairns on 18 Dec, 2023, 14:29
Quote from: Derek996 on 18 Dec, 2023, 14:16
My B32 will only do 55 mph max in top gear despite the engine being in very good condition, the timing accurately set and the carburation good. I understood why a couple of months ago when I was looking at the specs for the various BSA pre-unit singles and realised that my bike has a 19 tooth engine sprocket fitted by a previous owner but should have a 17t. It has been pulling B33 gearing. No wonder it wouldn't go any faster. I have a new 17t ready to fit over the winter.
My bike is a 1953 BSA B31 S, it also has a 19T engine sprocket but I'm nearly sure that is the correct one. The rear break hub sprocket is 42T
Cheers
Apologies, engine sprocket is 17T and gear box sprocket is 19T
Brian
Well since the gearing is correct it must be down on power for some reason. Since the timing would appear to be correct a compression check might be in order. One other thing: Are any of the brakes binding? Although you'd probably notice that just pushing the bike around.
Quote from: Derek996 on 18 Dec, 2023, 18:53
Quote from: briancairns on 18 Dec, 2023, 14:43
Quote from: briancairns on 18 Dec, 2023, 14:29
Quote from: Derek996 on 18 Dec, 2023, 14:16
My B32 will only do 55 mph max in top gear despite the engine being in very good condition, the timing accurately set and the carburation good. I understood why a couple of months ago when I was looking at the specs for the various BSA pre-unit singles and realised that my bike has a 19 tooth engine sprocket fitted by a previous owner but should have a 17t. It has been pulling B33 gearing. No wonder it wouldn't go any faster. I have a new 17t ready to fit over the winter.
My bike is a 1953 BSA B31 S, it also has a 19T engine sprocket but I'm nearly sure that is the correct one. The rear break hub sprocket is 42T
Cheers
Apologies, engine sprocket is 17T and gear box sprocket is 19T
Brian
Well since the gearing is correct it must be down on power for some reason. Since the timing would appear to be correct a compression check might be in order. One other thing: Are any of the brakes binding? Although you'd probably notice that just pushing the bike around.
Hi brakes not binding , so will try compression check.
Thanks for your help
Brian
Have ypu checked for free play in the cable of the valve lifter.
Does the mag advance the same amout by hand with the cable disconnected?
Quote from: cdsdorset on 18 Dec, 2023, 19:34
Have ypu checked for free play in the cable of the valve lifter.
Does the mag advance the same amout by hand with the cable disconnected?
Hi
I take it there should not be any free play on valve lifter cable?
Apologies ( I am only really starting my own mechanics) but what do you mean by "Does the mag advance the same amout by hand with the cable disconnected?"
Apolgies again
Brian
You need a small zmout of free play on the lifter cable. If its dead tight you could be just lifting the valve off the seat.
Take the advance cable off the mag and move the advance unit fully to both clockwise and clockwise directions and mark the mag casing at each position.
Then refit the cable and repeat. See if you get full movement with the cable fitted.
Quote from: cdsdorset on 18 Dec, 2023, 22:04
You need a small zmout of free play on the lifter cable. If its dead tight you could be just lifting the valve off the seat.
Take the advance cable off the mag and move the advance unit fully to both clockwise and clockwise directions and mark the mag casing at each position.
Then refit the cable and repeat. See if you get full movement with the cable fitted.
Thanks will check that out
Quote from: briancairns on 18 Dec, 2023, 22:56
Quote from: cdsdorset on 18 Dec, 2023, 22:04
You need a small zmout of free play on the lifter cable. If its dead tight you could be just lifting the valve off the seat.
Take the advance cable off the mag and move the advance unit fully to both clockwise and clockwise directions and mark the mag casing at each position.
Then refit the cable and repeat. See if you get full movement with the cable fitted.
Thanks will check that out
Lifter cable is fine, I will check the advance cable after Christmas.....as i also have to fit a rear hub sprocket and gear sprocket along with a new chain.
Thanks again
Brian
I think you are supposed to lay on the tank to get top speed...!
Can you adjust the timing for a peak in revs, when the engine is idling. That will be the best setting for starting the engine.
I hope you are timing from when the points start to open, not when they start to close..?
Is the carb slide definetley being pulled all the way to the top.
Quote from: scifi on 19 Dec, 2023, 09:46
I think you are supposed to lay on the tank to get top speed...!
Can you adjust the timing for a peak in revs, when the engine is idling. That will be the best setting for starting the engine.
I hope you are timing from when the points start to open, not when they start to close..?
Yes starting timing when ponts opening
Quote from: cdsdorset on 19 Dec, 2023, 10:00
Is the carb slide definetley being pulled all the way to the top.
yes but a bit sticky, need to check cable route
Thanks all for your help.
I will look at everything again after Christmas and let you know what happened.
Cheers
Brian
Brian,
In my view your engine should probably start on full retard, but most people recommend a little advance for starting.
I agree that it should almost certainly kick back on full advance.
Hopefully, Father Christmas will put a Neon tester in your stocking, and you will then be able to see if the magneto is sparking on full retard, and whether it is much brighter on full advance and very dim on full retard.
I agree with Julian, sounds like a weak spark.
You say the magneto is new, more likely, it's just been overhauled. Unfortunately, I have to tell you that I have had quite a few magnetos rewound by professionals, and had them fail shortly after.
If you want to go further, you could invest in a Spark Gap Tester (as I always say), then you will know that there should be a spark under compression (but don't test it with more than a 5/16" gap).
Assuming your spark is good, it could simply be that the ignition timing is too far retarded. If you're new to all this, are you sure you're following the correct procedure? For example, setting the timing on full retard rather than full advance? I assume you're using a fag paper, and checking it again after you have tightened the drive pinion nut? Are you using a rod down the plug 'ole or a degree disc?
Further to Scifi's suggestion, I understand that if you take all your clothes off while laying prone, you go faster still, but you may want to wear a Jock Strap just in case.
It has been suggested to me (please correct me if you can show that I am way off track) that if you have a slightly weak magneto (failing magnets, poor slip ring, excessive air gap failing coil insulation, poor capacitor and dirty contacts etc) that you need to consider the flip point of the rotating coil in the magnetic field where the output of the coil is at its maximum. This can manifest itself when you retard the ignition fully and you are behind the flip point (ie no longer in the peak phase of the output cycle and you get a weak signal) when the points open. This can be an issue if a clockwise mag is repurposed for an anticlockwise application (when looked at from the drive end ie timing cover).
(https://www.bsaownersclub.co.uk/forum/proxy.php?request=http%3A%2F%2Fwww.brightsparkmagnetos.com%2Ffaqs%2FFAQs%2520about%2520magnetos%2520generally%2FTiming%2520side%2520layouts%2FTiming%2520side%2520layouts%25201.JPG&hash=9f0ea6fc161c3b571f44f70bbae27542d8c9c9bb)
The BSA magneto for a b31/3 is an anti-clockwise (you will see and arrow on the A shaped cover plate on the mag, but of course these things have often been rebuilt and repurposed many times over the years but if the builder has not allowed for this you may get a good spark when advanced (ie in flip point) or weak spark retarded (outside flip point).
Once the engine is running you are more likely to get a decent spark but if you are not giving the engine a good swing for 500rpm to start up then a weak and ineffective spark is the result.
Quote from: neil1964 on 23 Dec, 2023, 10:16
It has been suggested to me (please correct me if you can show that I am way off track) that if you have a slightly weak magneto (failing magnets, poor slip ring, excessive air gap failing coil insulation, poor capacitor and dirty contacts etc) that you need to consider the flip point of the rotating coil in the magnetic field where the output of the coil is at its maximum. This can manifest itself when you retard the ignition fully and you are behind the flip point (ie no longer in the peak phase of the output cycle and you get a weak signal) when the points open. This can be an issue if a clockwise mag is repurposed for an anticlockwise application (when looked at from the drive end ie timing cover).
(https://www.bsaownersclub.co.uk/forum/proxy.php?request=http%3A%2F%2Fwww.brightsparkmagnetos.com%2Ffaqs%2FFAQs%2520about%2520magnetos%2520generally%2FTiming%2520side%2520layouts%2FTiming%2520side%2520layouts%25201.JPG&hash=9f0ea6fc161c3b571f44f70bbae27542d8c9c9bb)
The BSA magneto for a b31/3 is an anti-clockwise (you will see and arrow on the A shaped cover plate on the mag, but of course these things have often been rebuilt and repurposed many times over the years but if the builder has not allowed for this you may get a good spark when advanced (ie in flip point) or weak spark retarded (outside flip point).
Once the engine is running you are more likely to get a decent spark but if you are not giving the engine a good swing for 500rpm to start up then a weak and ineffective spark is the result.
Apologies Steve, i am only seeing this. My friend who knows alot more about mechanics than I is looking over the bike next week....I will let group know what I'm doing wrong ( no doubt) . thanks for your help
Brian
Quote from: neil1964 on 23 Dec, 2023, 10:16
It has been suggested to me (please correct me if you can show that I am way off track) that if you have a slightly weak magneto (failing magnets, poor slip ring, excessive air gap failing coil insulation, poor capacitor and dirty contacts etc) that you need to consider the flip point of the rotating coil in the magnetic field where the output of the coil is at its maximum. This can manifest itself when you retard the ignition fully and you are behind the flip point (ie no longer in the peak phase of the output cycle and you get a weak signal) when the points open. This can be an issue if a clockwise mag is repurposed for an anticlockwise application (when looked at from the drive end ie timing cover).
(https://www.bsaownersclub.co.uk/forum/proxy.php?request=http%3A%2F%2Fwww.brightsparkmagnetos.com%2Ffaqs%2FFAQs%2520about%2520magnetos%2520generally%2FTiming%2520side%2520layouts%2FTiming%2520side%2520layouts%25201.JPG&hash=9f0ea6fc161c3b571f44f70bbae27542d8c9c9bb)
The BSA magneto for a b31/3 is an anti-clockwise (you will see and arrow on the A shaped cover plate on the mag, but of course these things have often been rebuilt and repurposed many times over the years but if the builder has not allowed for this you may get a good spark when advanced (ie in flip point) or weak spark retarded (outside flip point).
Once the engine is running you are more likely to get a decent spark but if you are not giving the engine a good swing for 500rpm to start up then a weak and ineffective spark is the result.
Apologies Neil, i am only seeing this. My friend who knows alot more about mechanics than I is looking over the bike next week....I will let group know what I'm doing wrong ( no doubt) . thanks for your help
Brian
Hi all,
Finally got bike sorted.
The problem was my own stupidity .
I did not have engine tiiming set up correctly---too retarded, that along with a small tweak to carb .
Bike now going fine, except for a gear box issue which I will put into a differnt thread.
Thanks so much for all your invaluable advice.
Brian
With whole respect You owe us top speed, right?