Honda Dream CA77 305 Points and Timing Walk-Through
That particular gap coincides with the correct 'Dwell Angle' the period of time that the points are closed allowing the current to flow through the coil primary windings to build up the magnetic field. In the real world .013 to .015 will work, using a dwell meter is the most accurate.
1977 CB400F
1973 CL175 1976 XL175 - Sold 1964 CL72 1966 CA78
ScienceSo here's my guess / understanding.
When the points open, the current begins to build up from spinning dyno. The dyno has magnets spinning inside of coiled copper wire, inducing an electric field, and creating current flow in the wires. It keep building in the circuit until the circuit is broken (the point contacts open) Once the contacts open, the easiest path for the current to flow is through the spark plug, and this creates the spark. If the points were closed for too long, then maybe there isn't enough time for the current to fully discharge through the spark plug, and if they were open for too long, then maybe there isn't enough charging time for the circuit when the spark plug is not the easiest path. Comments? '64 CA77 305 Dream
It's as Malcom says. With closed points current flows through the primary part of the ignition coil. When the points open the current in the coil collapses and the coil momentarily becomes a transformer.
The spark plug is in circuit with the secondary part of the coil and this has many more turns. Just like a normal transformer, the ratio of turns causes a voltage amplification and this causes a voltage of around 6000v across the plug points which is enough to jump the gap. The points gap is just a convenient way of setting the "build-up" time which is the dwell angle. G '60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F Please excuse me while I resurrect this thread...
First of all, what a great post! THis has taught me a lot about how to adjust my points. But, I ran into a problem... My light is turning on as the "Golden Pointer of Justice (lol)" reaches the grey dot before the "f" mark. But unfortunately, I cannot adjust any further as my points plate is already fully turned in the clockwise direction. Could this be the cause for the kick back that I sometimes experience when trying to start the bike? Could this also be the reason why my bike seems to be running way rich (not fully igniting the gas in the cylinder)?
Last edited by stepper on Fri Jul 15, 2016 12:55 am, edited 1 time in total.
After looking carefully at my points, I have found that the ones on my bike look exactly the same as Paperslammer's. It has the "Denso" stamp on the backing plate and the shape of the arm looks to be of the Denso type as opposed to the Kokusan type points.
But after using this method of timing I still seem to be having early ignition with no more room to adjust/rotate the plate. So now I am thinking that I need Kokusan type points instead of Denso. So can I just switch out the points themselves or do I need to get the entire assembly including the backing plate? Also, does anybody know how to tell if your CA77 is a candidate for the less common Kokusan points? Was there a particular year or VIN range that used Kokusan? Thanks for any help! Before offering some suggestions for you to try, if you're static timing the bike (engine not running) be sure to use the timing line closest to the TDC line. In other words, the points should be opening almost at TDC (top dead center = piston at very top of stroke). The line furthest away from the TDC line is for timing with a strobe light.
Couple things you can do if the points are still opening too early even with the points plate fully rotated in the clockwise direction 1. Remove points backing plate and file/grind away some material to allow the plate to rotate further in the clockwise direction. 2. Reduce the points gap slightly. This will also cause the points to open later. (dwell won't be so wonderful, but it'll get you down the road) 3. You could also very slightly bend upwards the fixed points contact. Then re-dress the points contact surfaces to make them parallel, sort of.... (ditto the above) Remember to put a very small amount of grease on the points cam to reduce wear at the points rubbing block. The reason you're running out of adjustment is because the rubbing block on your points is worn down. I did the above to my Dream and it runs fine. Rode it to work yesterday. Doesn't hurt to have a store of guerilla repair tricks, they can get you home when others remain stranded! Do what you've always done and you'll get what you've always had.
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