The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => Lucas, Ignition, Charging, Electrical => Topic started by: bikerbob on 21.05. 2022 14:57
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I am grateful for all the replies that I have had about my magneto problem but at the moment I am at my wits end trying to sort it out.
Going back to the start of this problem after the winter lay up I serviced the bike as usual, took the bike for a short run just to see if all ok maybe 4 miles noticed that it was missing slightly when changing up put this down to maybe old fuel. Put fresh fuel still missing so thought it was a fuel related problem bought new set of carb gaskets stripped carb completely cleaned out jets etc carb was clean inside blew through holes with compressed air rebuilt carb fitted back to the bike checked fuel lines and also float level all OK.
Decided to take bike for a longer run was Ok for about 10miles just missing slightly on changing up but ran perfectly at about 45 to50mph, then things started to get worse the missing got worse and eventually could not open the throttle above a fast tickover or it would cut out. I was about 5 miles from homeit was a struugle to keep the bike running especially when trying to pull away at junctions or traffic lights, if I had to pull away on an incline I would never have got enough revs up to pull away. Eventually got the bike home, next day in the garage the bike started first kick but would not run above a fast tickover.
Having eliminated a fuel problem I turned to the magneto and fitted acouple of those red spark testers between the plug caps and the plugs kicked the bike over and it was sparking most of the time but it was missing on both cylinders and when you put the plugs together I am sure that at times both plugs sparked at the same time.
Decided to buy a refurbished magneto when it came looked great just like a new magneto everything inside has been renewed you can see new slipring new points and cam ring newpick ups. But when I fitted it to the bike it would not start when I checked the points gap thhere was about 9to 10 thou difference contacted the guy I bought it off he apologised I sent it back he has sorted the problem out retested the magneto and says it is now OK It came back this morning I checked the points and there is no noticeable difference int the gaps.
Set the timing a number of times but the bike will not start set it up with a degree disc at 35 BTDC. Without taking the timing case off I have checked the timing the old fashioned way with a rod down the drive side plug hole and on the compression stroke turning the wheel back and bringing it up to 5/16" turning the pionts to full advance the timing is correct. It does after a few kicks spit back as if the plugs were on the wrong way round tried swapping but no difference will not start. So what am I doing wrong, I have timed numerous bikes over the years but never had anything like this.
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Still need to check the basics :
1 check for spark
2 Kick over 10 times and remove plugs and make sure they are wet with fuel
3 Check compressions
If all 3 elements are positive - re-check timing.
After that - buy a Kawasaki *smile*
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Take one plug cap off and try running it on one cylinder.
If it fires but stalls again when you put the cap back on it's probably your slipring that's carbonised by the (to soft) brushes
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Hi Bob
I bet that the plugs are dead from the previous not starting issues
Try some new ones.
I have found NGK's die for the smallest reason *eek*
John
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Thanks again fo r replies The slip ring is brand new as are the pick ups this was done when the mag was refurbished and the plugs are sparking but just to be sure i did fit new plugs and did a continuity test on the leads. The magneto is sparking OK when turned over with the kickstart, and I have checked doulble checked and triple checked the timing and it appears OK it will just not attempt to start and even if I had the timing off say a couple of degrees it should still start. or at least try to start. All I get after nuemerous kicks is sometimes a spit back which you get if the plug leads are on the wrong way round but have treid changing to no effect. Over the years I have had other bikes Royal Enfield Norton and BSA all with magnetos and I have had problems before and stripped and replaced parts such as bearings cam rings and armatures points and you mightwell ask why I did not do this with the old magneto but I don't know I just thought I would take the easy route and buy a refurbished magneto.
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Presumably you've not fallen into making the mistake we've all made at some point and inadvertently timed it after TDC?
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Once I have determined the compression stroke by finger over the plughole I put the bke ingear and turn the back wheel forward to TDC then turn the wheel backwards to below the required pisto n position and then carefully turn the wheel forward until piston is at correct position for timing set points to just opening with the usual fag paper jam auto unit to full advance fit to magneto then turn engine over repeat to check that timing is correct.
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Hi Bob
Have you tried some fresh petrol?
when it goes a bit stale starting becomes an issue
John
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Sounds fuel related, try with the tank cap off
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Petrol in the tank is only a couple of weeks old and I have established that it is not fuel related carb completetly stripped cleaned and rebuilt fuel lines checked float bowl level checked no blockage in petrol cap. Also have established that the old magneto was at fault by fitting spark testers between plug caps and the plugs and it showed that the missing was on both cylinders. Tomorrow I am going to set the ignition timing by using the BSA recommended proceedure as stated in service sheet 203 up dated 1966 which recommends using the gear side piston and removing the valve covers and checking that both valves are closed. this will guarantee that I am on the right compression stroke. It will also give me a chance to check valve clearances as I have not checked them for a couple of years.
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The slip ring is brand new as are the pick ups this was done when the mag was refurbished . . .
Posted this a couple of days ago . . . but in the wrong post *conf*
It's a copy of a letter I sent to Wassell a few years ago after discovering new Lucas brushes were a problem. In the end got replacements from Brightsparks Magnetos and I've not had a problem since. (Left click to read).
Rog.
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Well worth posting again Rog 'cos these cheap nasty soft brushes cause a multitude of problems and yet it's simplicity itself to rectify. - Maybe should be a warning banner at the top of the home page.
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I can lend you a magneto... Just PM me or give me a ring at Priory Magnetos.
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This morning decided to start again from scratch setting the timing as per BSA service sheet 203 this involves removíng petrol tank and valve covers setting TDC by ensuring that both valves are closed on the correct cylinder, went through the usual process of setting the piston position and correct points setting and fitting auto unit jammed full advance. Bike will still not start after about 5or 6 kicks you get a backfire through the exhaust tried swapping plug leads still getting backfire in exhaust. Then decided to remove refurbed mag fitted the old faulty mag timed it and bike started first kick but with the old problem that is missing and when you open the trottle it gets worse and then cuts out. Rang the guy I bought it off he told me how he tests them on his set up rig runs them for about 4 hours then makes sure the spark can jump a 6mm gap. I replied that OK but even with a good spark it will not start the bike and he could give no explanation why the old faulty mag will start the bike but the refurbed one will not have now agreed to send the mag back and get a full refund. Now going to leave everything for a few days and then decide what I will do next.
Just seen your post CheeserBeezer thanks for the offer but I am going to take time away from this for a few days then decide what to do I may go down the electronic route or stay with a mag I converted my A65 to electronic ignition some 10 years ago and has run well with no problems I know different bike with no mag but no problems only you have to have a decent battery and coils for the A7
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G'day Bob.
This may be a silly question but are you putting the atd on fully advanced with the points at 12 thou" or just opening with a fag paper?
Cheers
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Bob.. The fact that the bike starts and runs with the old magneto would indicate that the engine is basically sound mechanically. The refurbished replacement magneto is not up to the job for some reason.
But with the supplier willing to give a refund, this leaves the scene and we are back to the start. Andrew's offer of a short term loan would prove if the fault resides within the fuel system. I have every faith in his reputation, and feel sure that he will assist with practical advice as well if necessary.
The number one problem with an old temperamental magneto is the fragile and penny pinching electrolytic capacitor (Condenser) buried within the armature. The symptoms you have of good cold starting then later failure would be a pointer to a problem here.
These days there is a cost effective solution from Brightspark Magnetos, which is another avenue to consider if you want to stick with old school ignition rather than moving to electronic, such as the Thorspark system which employs the duff magneto as a carrier, using what you already have and in the grand scheme of things is a reasonable choice.
Swarfy.
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"Penny-pinching electrolytic capacitor"?
It's lasted 60 years, so how much longer should it be expected to go on working for? ;)
Another vote for the Bright Spark replacement capacitor (I have them on three of the fleet) but wasn't keen on the Thorspark set-up although many seem to find it works great.
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Hi Bob, I feel your frustration. I don't know where you are in the UK but, if you were round the corner, I'd bring a mag, fit it for you (in about 40 minutes), and send you off over the horizon with a smile on your face. It is often the case with old bikes, and in life generally, when something goes wrong we solve the problem by circumnavigating it (electronic ignition = divorce) rather than persevering. Going down different avenue (remarriage?, though thankfully I don't speak from my own experience!) only brings about a different set of problems. The original design of the A10 worked well for those who looked after their bikes (changed the oil = bought them flowers) and it is difficult to improve on what the manufacturer did in the day. If your mag supplier is refunding you then you can buy one of mine....which will be cheaper.... and it will work....and if it doesn't I will personally come and fit another until you are 100% happy.
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That must be the deal of the century, Andrew.
Well done.
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I'd definitely replace the spark plugs. Modern unleaded gas produces a very fine and highly conductive carbon when it fouls. I've put plugs on a mains powered megger and had them produce a bright white light as the carbon burnt off. Not good for the megger probably but interesting as the plugs looked completely clean but were giving a very uneven performance in the bike. Two mags with the same result would tend to suggest the problem lies elsewhere. I had a fault plug cap that caused a similar problem once that I only spotted when running the bike at night.
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Speaking of plug caps, remember we shouldn't use resistor caps (which most are these days) on a mag sparked bike. I posted a while back the figures of how they beat up a mag - here's a copy. Believe is was from Brightspark. Note how they reduce the spark and increase voltage in the mag.
without suppressor with 4.6kO suppressor difference
peak voltage to initiate spark 9,600V 10,600V @ magneto
9,300V at plug -3.10%
DC component of HT current after striking spark 53 mA 52mA -1.80%
DC component of HT voltage after striking spark 910V 1,160V at magneto 27.30%
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i once used supressed plug caps but didn't know they were until a chap told me to get them off and sod upsetting the neighbours tv's *whistle* i took them off the next day and found out they could damage maggy *bash*
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I contacted Andrew at Priory Magnetos and sent my mag off to him he rang me to say that there were problems with it namely the armature had been rewound before but it was an amtuerish job and the capaciotor was of a type that has not been used for some years because they were not reliable and one of the pick up brushes was too soft. he refurbished the mag it is now fitted to the bike and it now runs perfectly. So if anyone has a mag problem they can do no better than to contact Prory Magnetos they will get first class advice and an excellent job done.
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Very kind remarks. Thanks, Bob.