I have a 1970 BSA A65 Thunderbolt, it is fitted with a Boyer Ignition (I put the Boyer in about 10 years ago). The bike starts up fine in the morning, but after about 2 minutes on the road the engine will stop running almost like the ignition has been switched off. The lights work fine and continue to work when this happens, the battery is fairly new and in good shape. It will not start for about a minute or two and then will re-start and run just fine. Once the bike has gone through this, it runs and starts fine unless it sits overnight or until it is completely cooled off. It can sit for an hour or two and will not do the 2 minutes and die routine. It also seems to only do this when it is cold outside in the morning. After a ride to work, in the afternoon ride home, I have not had this problem. I've checked the wiring connections to the ignition system, checked the ground connections, checked the battery connections, spark plug wire connections at the coils, anyone have any other ideas?
I had the same problem with my Boyer on my A65. It would run for 90+- seconds and then quit. It would start right on the next try. My problem was the kill switch I had put in the circuit too much resistence in the circuit???. I didn't find this out until much hair pulling and experimentation I removed the interupt switch and that solved the problem. BTW I reconfigured the kill switch to the proper circuit and it works fine. I would suggest a good look at the ignition/wiring system. Steve in Ohio
With 13 volts measured with the lights and ignition on, and engine not running, - I would suspect the voltmeter.
If another voltmeter shows similar results then I would be having another good look at the battery. 15 volts running is also too high. So if the voltmeter you are using is in fact telling the truth, then the charging circuit could be overcharging the battery, the Boyer could be reacting to that. Holy,... between 13 and 15 volts with the lights on, Some of the guys on this forum would kill for a circuit like that. How bright are your lights ? I believe the Zener should kick in at about the 14 volt mark so you should never see any higher than that. It is normally accepted that with the lights on, and normal riding speeds, the bike should settle out somewhere in the low 13 volt region. I would certainly try to fit another (borrowed) battery and see what happens then also.
I am having the opposite at the moment. My B50 is starting with the battery disconnected (Good old Boyer) but the battery is too far gone to charge for the next start. I have connected the battery up just after starting and it runs fine until I shut down. At least I know I just need to find another battery.
The lights are very bright, and compared with my other 12v bike about the same. The 6v bikes I have are much dimmer. I use an old Simpson analog meter and it may not be exact, but it's all I've got. My charging system consists of the original alternator, rectifier, and zener diode. I use a gel cell battery similar to one posted on this message board recently. I'll try to get hold of a digital meter and see what it reads. I've also checked the grounds and they seem to be good, I sanded off the paint down to bare metal where the grounds are and used dielectric grease at the connections.
Interesting that it was mentioned that some people would kill for 13-15 volts on their bikes, I have a '51 BSA Bantam that had a serious problem buring out 6v bulbs, and the only cure was to run 12v bulbs. When I asked a Bantam parts supplier in England what the problem was, he said "you got a good one".
Maybe a long shot, but I had a wire in the ignition circuit (actually the jumper between the two coils) that was broken inside the insulation, such that only one or two strands of wire were still connected, and my A65 exhibited the same symptom. Apparently the one or two strands of wire conducted enough current when cold, but in so doing generated heat, and eventually became hot enough to not conduct. I eventually noticed a "limp spot" in the wire and I carefully cut away the insulation to find the partially broken wire and signs of scorching.
I also had a similar problem with a corroded spark plug wire - worked fine when cold, but not when hot.
Thanks to all for the ideas on where to look for problems, plus the encouragement. In my last round of checking wiring, etc., I replaced the spark plug leads, made sure I had a good ground from the cylinder head to the frame, checked the connections from the Boyer stator plate making sure they were perfect, re-checking spade connections, and I also checked the vent in the gas cap and cleaned out the float bowl on the carb. The problem is now gone, but exactly what was the cause I do not know since I made so many corrections and checks all at once. I never did get hold of the digital voltmeter, but putting on my reading glasses and looking closely, it looks like the battery is putting out 12.5 volts with the lights on, at the battery terminals, and at the white wire going in to the Boyer. It goes up to 14 when the engine is revved up. I certainly learned a lot about the Boyer system, and some things about British electrical systems I did not know!
RF, how does one join the GABMA? I clicked on the link for membership but it did not work.