The standard points gap used by Lucas on any of the coil ignition distributors in the 60's & 70's for bikes and cars was 15 thou with the earlier 12 thou figure a throwback to magnetos. Later on they used to specify dwell angle rather that points gap. If a distributor requires a larger gap then the problem is with the points not operating correctly or a soft heel wearing quickly and so its the replacement points that are the problem and not the gap. The other problem with replacement points is the closing spring can be wrong spec and so the points end up floating which again can be masked by opening the points wider. Also look for badly made cams and cams that can move due to worn distributor & bearings and even a bent shaft in the distributor.
I had a Triumph car years ago with 6 cylinders and one set of points set to 15 thou and one condensor and that car could rev to 6000 rpm and the single condensor worked fine. The recharge time of the condensor is perfectly capable of coping with firing 6 cylinders so two cylinders for our bikes is not a problem. In fact opening up the points gap potentially reduces the time that a condensor has to recharge. The recharge time is all to do with the value of the capacitance of the condensor and the inductance of the ignition coil and can be calculated. Its basic electrical / electronics theory which I used to use at work.
As Tim says, if you alter the points gap you also alter the set ignition timing so opening the points to 25 thou to compensate for a badly wearing heel will cause other problems because as they wear and the points gap closes then the ignition timing will retard itself at the same time and this can be by quite a few degrees.
I have been running a system just like the initial posting on my Rapide for over 25 years and have had no problems running at the specified 15 thou. Like Roy suggests though I run two condensors and two seperate ignition coils and the reason for that is if a coil or condensor fails I can still run on one cylinder and get home.
The solution is to find a decent set of points and decent manufacture condensor which is difficult today as no new vehicles use such an ignition system anymore. Most new condensors/ points today are made in China.
Simon
I had a Triumph car years ago with 6 cylinders and one set of points set to 15 thou and one condensor and that car could rev to 6000 rpm and the single condensor worked fine. The recharge time of the condensor is perfectly capable of coping with firing 6 cylinders so two cylinders for our bikes is not a problem. In fact opening up the points gap potentially reduces the time that a condensor has to recharge. The recharge time is all to do with the value of the capacitance of the condensor and the inductance of the ignition coil and can be calculated. Its basic electrical / electronics theory which I used to use at work.
As Tim says, if you alter the points gap you also alter the set ignition timing so opening the points to 25 thou to compensate for a badly wearing heel will cause other problems because as they wear and the points gap closes then the ignition timing will retard itself at the same time and this can be by quite a few degrees.
I have been running a system just like the initial posting on my Rapide for over 25 years and have had no problems running at the specified 15 thou. Like Roy suggests though I run two condensors and two seperate ignition coils and the reason for that is if a coil or condensor fails I can still run on one cylinder and get home.
The solution is to find a decent set of points and decent manufacture condensor which is difficult today as no new vehicles use such an ignition system anymore. Most new condensors/ points today are made in China.
Simon