SOTP Vintage Series
Main Motorcycle: The one between my legs
Join Date: Feb 2009
Location: Upstate NY
Other Motorcycle: A few
Extra Motorcycle: Yes
Interesting... I just went thru the same set of problems with a Type I Honda 305 Scrambler. Solved the problem today.
The points should not arc excessively. If they do, that's normally an indication that the condensor is bad. However, if they are contaminated, and the conductivity of the contacts is marginal, then you might see arcing.
Here are some tests to perform.
Disconnect condensors and test them for a dead short to ground. They should charge up from your DMM and then show in essence an open circuit to ground.
Put a light on your points as if you were going to static time the engine. One clip on the coil side of the points and the other to a suitable ground. If the light comes on and stays on as you turn the engine, chances are you have a bad set of points.
Take a piece of emery paper, fold it so you have grit on both sides and with the points closed, open them with your fingers insert the emery and clean them. When finished blow off the points with compressed air and then clean them with a piece of cardboard soaked in acetone or lacquer thinner. Slide the cardboard back and forth and then put a dry piece in there and make sure it comes out clean. A dollar bill is also good for removing the grit. The fabric used to make dollars will let the grit embed in it.
Now retest with your light.
Also open, clean and test all your connections between the coils and the points for continuity and good connections.
Also check the hot side of the coils to make sure you have 12V on each coil with the ignition on. Make sure that wiggling wires does no interrupt the 12v to the coils.
My problem started with a left cylinder that would not fire, but once the bike warmed up, it ran perfect. Did a two day event with the bike and each morning it started on one cylinder and after some warming up, ran on both.
First investigation revealed bad arching on the points. Assumed condensors (original 1967 vintage parts) were failing from moisture (event run in two days of rain). But condensers tested fine. Pulled everything apart, cleaned all the terminals, tested all the wires, reassembled and problem changed sides. Now right side would not fire. I knew I had put everything back where it was so not a case of swapping sides with coils, condensors, etc.. But it was late and decided to call it a night. Started on it again this morning and found that one of the points that worked fine when I static timed the bike was now not making good contact. I had to pressed the points with finger pressure to get the timing light to go out. So this time I really went at the points contacts with emery and then cleaned them thoroughly with acetone. Bike runs like a raped ape now.
What I think happened was the PO had put an excessive amount of grease on the points cam and I think that it had coated and baked on the points. Or the points were severely corroded and need more than a quick touch up with emery. The serious polishing and cleaning did the trick. Will still put new points in engine and probably a new consensor pack. But only time will tell if today's fix will last with the present components.
Do do hit and miss troubleshooting. Go piece by piece. you can swap plug leads and coils to see if the problem changes sides as a quick check. Then work your way thru the pieces. You'll find it. It might just be a faulty/high resistance connection.