Honda used conventional points and condenser ignitions on all of their bikes until about 1978. Nippon Denso was their primary supplier, however, Kokusan and Hitachi components were also used for various ignition and charging system applications. Nippon Denso has ND stamped somewhere on the points base and base plate, as well as on the condensers. Kokusan parts often have a K and Hitachi used either an H or one of their Kanji-based manufacturing marks. Later four-cylinder models used TEK ignition contact sets.
Please note that none of the various branded point sets will interchange with the others. All have unique point plates and methods of adjustments. Many of the replacement points sets available now come from a company called Daiichi who attempted to copy all of the other brands. In some cases, particularly for Honda Dreams, the attempt fails to match the OEM or original manufacturer’s dimensions. I would recommend searching for the original branded point sets or whole point plate assemblies rather than get caught up in the aftermarket branded replacements.
Point cams, which open and close the contact sets are placed in numerous locations, depending upon the engine configuration. Most Honda 50cc Cubs used a magneto ignition, with points and condenser packed beneath the flywheel. The electric-start C102 had a battery ignition system, however. The early pushrod singles all had flywheel-mounted ignitions, as did the 125-150cc Benly twins. Honda's prolific 250-305 twins had a points plate mounted off the right side of the camshaft cover, however, the actual points cam design included a long shaft that tunneled through the hollow camshaft half with an engagement tang, which connected with the central cam sprocket. The160-175-200-350-450 twins all had a removable spark advancer unit, which bolted into the end of the overhead camshaft.
Dual-point sets fired twin-lead coils on the newer-generation 350-400-500-550-750 OHC fours, as well as the early model GL1000 Gold Wings,. All of these engines used the "wasted spark" concept when the spark plugs were connected to two cylinders of 180 degree apart firing sequences. All 250-305 Dreams and almost all 125-200cc twins used a single twin-lead coil, fired by a single set of points.
I have had many questions sent my way concerning bike engines that had either a slow return to idle condition or a continuously fast idle speed, wherein no amount of carburetor adjustment would effect a change to the condition. In the high percentage of cases, the mechanical spark advancers had sticking/frozen advancer cams, nearly welded to the central mounting shaft. Other spark advancer woes include advance weights with oval holes and broken/stretched or missing return springs. Most spark advancers are going to kick in 25 or more degrees of ignition lead when they are activated. When the spark timing advances that far, it changes the vacuum signal to the intake system, drawing more fuel/air than normal through the metering circuits, all of which causes the engine speed to leap upwards despite normal external "adjustments" to the carburetor idle speed screws. As a part of any tune-up procedures, always check the function and condition of the spark advance units, before blaming defective carburetion as the cause.
When misfiring occurs, any component in the carburetion, electrical and ignition system can be the cause. ALWAYS start with cleaning the ignition point contact faces. Lubricate the small felt lubrication pad with a couple of drops of oil and/or lubricate the points cam with special point cam grease. Once the contact faces are clean and parallel to each other, set the gap to approximately .014"-016" when the point rubbing block is up on the highest portion of the point cam ramp. This determines the "dwell" of the ignition coil, also known as saturation period. The ignition coil must have sufficient time to build up an electrical charge in the windings before discharge. If the points are opened too wide, there isn't enough time for them to be closed sufficiently for coil saturation.
When points are closed excessively, there is an increased tendency for them to arc, as well as another phenomena that occur on some dual-point applications. When the point gap is too narrow, there is a moment where both sets of points are momentarily closed, which causes the normally oscillating voltage/current distribution (alternating between the two sets of points) to be tapped by both coils at the same moment. The momentary "double-draw" on the B+ primary feed wire, reduces the available current/voltage to each coil by half. When this happens, both coils are underfed and the maximum voltage output on the secondary windings is greatly reduced. Peak voltage requirements are often when the throttles are cracked open during acceleration. When the momentarily lean air/fuel mixture is inhaled and compressed for firing, a substandard voltage level will cause a BIG misfire/hesitation. ALWAYS ensure that both sets of points are independently open AND closed during the firing cycles. Keeping the point gaps towards the .016" gap measurement will automatically prevent this occurrence.
Numerous other causes for misfiring include a weak/failed condenser and defective spark plug caps (cracked down the sides, causing arcing to ground) or failed internal 5k ohm resistors. Any damaged spark plug wires or spark plug caps not securely fastened to the wire ends add to the list of misfire causes due to ignition deficits. While Honda ignition coils seldom fail in regular service they are not immune from causing misfires when the internal secondary copper wiring either burns open or short across adjacent coil windings. Instead of doing proper trouble-shooting to determine a "no spark" or "weak spark" condition, owners often choose to blame the coil. After paying for this expensive component, they discover that the original coil was not the cause of the fault.
Care must be taken when replacing contact sets, as there is an intricate package of insulators to isolate the movable contact side electrical connections from grounding to the base plate. Placing the "flag terminal" against a grounded post will prevent the coil from firing. Even when the wire terminal is properly sequenced in the terminal connection, a little bit of mispositioning will have the corner of the terminal touching ground against the base plate or sometimes when the point cover is installed.
After 40-50 years of service, the point adjustment and mounting hardware is often damaged from use of ill-fitting screwdrivers. Be aware that pre-1968 hardware threads were JIS threaded, not the later ISO specifications. Any 3, 4 and 5mm screws are specific in their thread pitch.
3mm changed from .6 to .5
4mm changed from .75 to .70
5mm changed from .9 to .8
JIS thread screws are difficult to find, so re-threading the screw holes allows the use of the later ISO screws, which are readily available. For best results, find a new point plate assembly.
In the big scheme of things, points are just adjustable switches, which turn the ignition coils on and off during operation. Clean contacts, adjusted to proper specifications ensures proper ignition timing during all types of operating conditions.
Bill "MrHonda" Silver 11-2019
Well written, excellent information!ReplyDelete